I don’t believe that is sufficient. I understand MTS system generation depends on having a MODIFIED version of Assembler H.
That is correct. I don't think anyone has been able to assemble much of MTS without the MTS version of ASMH.
This may not matter too much in the current discussion since later versions of MTS only run on XA machines. XA was the current architecture when development of MTS ended so that's all that D6 supports. However all previous distributions of MTS are available online (see . I'm not sure offhand which is the last version supporting 360/67 or 370 (non-XA). This is documented somewhere but I'm not sure where. One of those versions should run in older versions of VM (or CP/67).