Hi:
      This unix system V Release 2 system disk image is not  theoriginal distribution.  This image is a make up one which build from a anonymous SYSVR2 usr file system in cpio format. This rebuilding process was on a  vax SYS3 system as the following steps:

1.  convert from cpio to tar format in a linux system
mkdir sysvr2
cd sysvr2
cpio -ivdm <sysvr2-vax_usr.cpio
tar cvf ../svr2usr.tar ./*

2. create simh tape format 
use the program maketap.c which can be found in PUPS archives.
then you got a simh format tape file : svr2usr.tap

3. mount svr2usr.tap on SYS3 system and unarchive in a new rp disk,then mount this rp disk in /mnt

4. in svr2usr/src/cmd 
    build some svr2 version programs in SYS3 execute format :
    we need the sys3-2-svr2 cross compile environment to cross-build the svr2 root system.
    to reach this aim we need the following grogram:
    sh : shell 
    make:  make tools
    cc:       c compiler
    c2:      c optimizer
    ar:       bin file format archiver
    ld:       loader
    as:       assembler
    nm:     
    strip:    
    size:  
    ccom
    libc.a
    crt0.o
    mcrt0.o
    cpp
    according the following priority (all those program were in /mnt/src/cmd) 
    note: only build do not install !
   1) in /mnt/src/cmd build sh, make 
   2) in /mnt/src/cmd/sgs directory
       first cd libld, then build libld
       then build ar, as, ld, nm, size, strip one by one
   3) in /mnt/src/cmd/cc directory build cc and ccom
       in cc.c need function tempnam which is a new function of libc in svr2, the libc of sys3 lack of such function , we should copy those contents from svr2 libc file (/mnt/src/lib/libc/port/stdio/tmpnam.c) 
   4)  in /mnt/src/cpp build cpp ( optional but suggested)
    ok, now ,we should copy those binary program to /bin and ccom and c2 to /lib with a suffix ".n" which make distinction with original program, and duplicate the orignial program to a new copy with a suffix ".o" 
    I write the following scripts to change between new compile env with old compile env
o2n:  old env to new env
-----------------------------------------------------------------------------
cd /bin
cp ar.n ar
cp as.n as
cp cc.n cc
cp ld.n ld
cp nm.n nm
cp size.n size
cp strip.n strip
cd /lib
cp ccom.n ccom
cp libc.a.n libc.a
cp crt0.o.n crt0.o
cp mcrt0.o.n mcrt0.o
cp c2.n c2
cp cpp.n cpp
cp libPW.a.n libPW.a
-----------------------------------------------------------------------------
n2o  :  new evn rollback to old env
------------------------------------------------------------------------------
cd /bin
cp ar.o ar
cp as.o as
cp cc.o cc
cp ld.o ld
cp nm.o nm
cp size.o size
cp strip.o strip
cd /lib
cp ccom.o ccom
cp libc.a.o libc.a
cp crt0.o.o crt0.o
cp mcrt0.o.o mcrt0.o
cp c2.o c2
cp cpp.o cpp
cp libPW.a.o libPW.a
------------------------------------------------------------------------------

 
   5) build new format libc in /mnt/src/lib/libc
       in this step, we should use new compile env (according step (4))
       after building completed, copy libc.a crt0.o mcrt0.o to /lib with a new suffix ".n"
       
     ok, from now on we have a complete cross-compile tool-chain which can build svr2 format execute binary in a SYSIII system.

5. to build a make-up SVR2 root file system
    svr2 file system was different with sys3.  the block size of svr2 file system is 1024 byte but the block size of sys3 is 512 byte. so we must build mkfs program by sys3 compile env (old env)
     cd /mnt/src/cmd  to build mkfs then copy to /etc/mkfs.n
     we make use of the feature of mkfs that  proto file system.
     then we use the following config file to create a proto svr2 root file system.
     But, the bad news is mkfs has some limit and bugs :
      1. can not copy file large than 64k, but the kernel is big than 64k. 
      2. can not make a complex file system.
     so, we only use this tool to create device file. the other jobs will be done by linux which has a sysv file system module. 
 /tmp/miniroot
     --------------------------------------------------------------
/stand/gdboot2b
 10392 4800
d--777 3 1
     console  c--644 3 1 0 0
     systty  c--644 3 1 0 0
     syscon  c--644 3 1 0 0
     mem  c--644 3 1 3 0
     kem  c--644 3 1 3 1
     swap b--644 3 1 0 0
     tty  c--666 3 1 2 0
$
     ----------------------------------------------------------------

then execute sysvr2 version mkfs to create new file system on a blank rp06 disk file
in simh 
set rp2 rp06
att rp2 svr2_root.img
in sys3
/etc/mknod /dev/rp16 b 0 16
this command to create rp2 device file in sys3 system
then run
/etc/mkfs.n /dev/rp16 /tmp/miniroot
 then 
sync 
then stop this machine ctrl+E
copy svr2_root.img to linux
to make linux has sysv file system module (reffer to google)
in linux 
mount -o loop -t sysv svr2_root.img /tmp/svr2
then in /tmp/svr2 directory, we can create final SVR2 root file system layout. and we can use this method to copy file from sys3 system to SVR2 image (exchange method between sys3 system with outside : in sys3, use dd to copy a file to a temp-rp disk file by assign exact block size "bs=12345" , then use dd to copy out of this temp-rp disk file in linux by assign the same block size as the original)
in /mnt/src/uts/vax directory, there are 3 kernel images, it is enough to boot up the SVR2 system.
then, we make the minimal root file, 
note: those program should use new cross-compile to compile from /mnt/src/cmd source file
/stand directory should build from /mnt/src/stand directory
/dev/
     console  c--644 3 1 0 0
     systty  c--644 3 1 0 0
     syscon  c--644 3 1 0 0
     mem  c--644 3 1 3 0
     kem  c--644 3 1 3 1
     swap b--644 3 1 0 0
     tty  c--666 3 1 2 0
/bin/
     sh
     ls
     cd
     cp
     dd
     pwd
     mkdir
/etc/
      getty
       init
       inittab
       login
       mount
       mkfs
       passwd
       rc
       group
/stand
        gdboot2b
        sash
        ls
        
6. some hacks
     the original gdboot2b (which boot from 1024 byte file system ) could not directly boot rp6 disk file. there might has some trick to make gdboot2b functional, but I have no idea about such trick. So , I have to modify this boot loader which is  a assemble language file.
in /mnt/src/stand/vax/boots
the following is diff file 
--------------------------------------------------------------------------
# diff gdboot2b.s gdboot2b.wu.s
1c1,2
< #     @(#)gdboot2b.s  1.5
---
> #     @(#)gdboot1b.s  1.4
> #     @(#)gdboot1b.s  1.4
15a17
>       .set    MBA0,0x20010000 #MBA 0 device reg's
57c59
< star: movl    0x5c(r11),r9
---
> star: movl    $MBA0,r9
59c61
< common:       addl2   r9,r10
---
> common:       movl    $MBA0,r10
208,216d209
<       .byte   0x17    # RM05
<       .word   608
<       .byte   32
<       .byte   0x10    # RP04
<       .word   418
<       .byte   22
<       .byte   0x11    # RP05
<       .word   418
<       .byte   22
220,225d212
<       .byte   0x22    # RP07
<       .word   1600
<       .byte   50
<       .byte   0x16    # RM80
<       .word   434
<       .byte   31
----------------------------------------------------------------------------------------------------
       
        
       
7. what on earth contents in /etc directory? 

    sorry, I don't know. I have to refer SYSV PDP11 /etc directory. in fact, I directly copy those text file (script, ascii data file, config file ) from PDP11-SYSV /etc to SYSVR2 /etc. And it sames works beautifully. 

Ok, Above all  were what I have done.