Have you tried mounting the CD after installation?
I presume the CD-rom a DEC CD that's jumpered for a 512-byte blocksize?

Did you  specify 

    mount -o ro -t cd9660 /dev/rz?a  /mount/point

(where ? is the appropriate SCSI unit; 4 is common on DEC hardware).

My guess is that the sysinst code is using the MI scsi names.  That
will fail the pmax port uses the old 4.4bsd scsi code, with /dev/rz?a,
not cd?a (e.g., /dev/rz4a not /dev/cd0a).

Maybe we can get this fixed for 1.3.3, but who knows if/when more CDs
will be pressed.

Simon: time for another doc update and FAQ entry...