Well... the only indirect command processor present on RSXM70.DSK was
ICX.TSK
I transferred it from simh RX50 disk image to a RT-11 formatted floppy
with PUTR (copy /binary) and then with FLX
FLX> DU0:=DU1:ICX.TSK /RT
Then
REM ...AT.
INS $ICX.TSK
@[1,2]STARTUP.CMD
and got a BIG system crash
So they are definitely not compatible.
I've got a 4.2 RSX-11M plus tape set.
I'll try to install it on simh and see if they are binary compatibles...