Device Block Mode is the biggest read/write compatibility
SCO 3.2v4.0 will probably default to 512 byte fixed blocks, while
OpenServer 5.0.4 will ask the tape drive for its default block mode,
which is 0 (variable) for some drives (HP Surestore) and 512 for
others, such as Wangtek.
Since "tape setblk" on 3.2v4.0 is broken, the best way to set the tape
drives to be compatible is, with a tape in the drive, to issue a
"tape -a 512 setblk /dev/xStp0" on the 5.0.4 system.
Reads and writes should then be compatible.