Hello MTS community! After some moderate reading and light usage of
MTS, I would appreciate if you could answer some of my questions.

1.) Now that archive.michigan-terminal-system.org has been down for
almost a year - though well-archived on Archive.org, and with the
Google Drive links still existing - will this mailing list be the only
home of the MTS community, or will there eventually be another website?

Yes, there will be a new web site. We were just talking about this today.

2.) Obviously not everything can be released for legal/licensing
reasons, and sorting thru it all for D7.0 will take however long it
takes.

But I would like to know: are these files picked out yet but
just not publicly available pre-usable-system, or are most of these
files still being negotiated with rightsholders/programmers/etc? (As
far as I've read many/most of the post-D6.0 redistribution tapes are
still lost, so obviously those can't be sifted through yet.)

All of the so-called "redistribution" tapes were lost. These were informal tapes shared among the MTS sites (sort of like Github without the internet). The rest of the stuff is still being sorted through.

3.) Is it possible to connect a VT52/VT100/Tektronix to the current
D6.0A? Or would that require the networking support in D7.0? (Vol. 4
Appendix B reads to me like UMnet needs to be functioning first.)

This is a complicated question and the answer depends on exactly what you want to do. Connecting a real glass teletype to MTS (i.e. a VT100 or something that emulates one) will be very difficult. However if you run MTS in Hercules you can connect a tn3270 client to MTS right now. Hercules turns a tn3270 connection into a local 3270 which MTS supports. You probably could hack together something that would connect a VT100 emulator to MTS, but I don't think anyone has tried this and I'm not sure how you would do it.

4.) Browsed through CCM 448 [1] about VSS. However, I still have a few
questions:

a.) What version of MVS/370 did support stop at? Can it run
programs for the venerable 3.8j?

Something old. I don't think any particular version was targeted and the emulation was not complete. Mainly it emualted anything needed by a program we wanted to run. It was never meant to be a complete emulation of MVS.

b.) Was there networking support?

No

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5.) I read the previous message about the HIM merge. Is this fork
publicly available?

No, not yet. Soon, I hope.

6.) There were several MTS systems on the BITNET network[1]. Looking
through the bitnet writeup (6.0T5 -1454), MTS BITNET supported
operation over multiple link protocols:

313 The full complement of RSCS link protocols will be
supported.
314 This requirement allows interworking with RSCS emulation
packages
315 which only implement a single protocol.

718 Link protocols (VMB, VMC, NJE, and X.25)

1166 At this writing, only the VMB DSP has been written at the
protocol
1167 layer and the SDA DSP at the physical device layer. In
addition,
1168 a subtasking monitor unit check routine for SDA device type
has
1169 been written.

1367 UBC and SFU have expressed a desire to implement their
Netnorth
1368 link using X.25 and Datapac, because bisync is not
available. It
1369 should be possible to substitute the UBCnet X.25 DSP for
either
1370 the SDA or CTCA DSPs to provide this function, in effect
1371 substituting a full duplex X.25 virtual circuit for a
permanent
1372 bisync line. The VMB or NJE protocols could then operate
over
1373 this link.

You will note that much of this is written in the future tense. At the time of D6 the Resource Manager (RM) was not yet integrated into MTS so none of this is available in D6. The 1996 system has the RM and it works well. I haven't tried BITNET since there is no one for me to talk to and configuring it is a pain. I have however gotten a Postscript printer on my local net to print from MTS using the RM.

Hyperion uses a 2703-lookalike[2] to tunnel NJE over TCP/IP. MTS also
supported the 2703[3], although it was eventually replaced with the
PDP-8 Data Concentrator[4], which was itself replaced with the PDP-11...

-----> The point: did the PDP-11 HIM/NIM/PCP/SCP/whatever support
NJE over a bisync line? Or was it TCP/IP, X.25, and local terminals
only? Would the 2703 be the only way to get BITNET on MTS, or
would an NJE-supporting frontend be the better option, perhaps in
combination with NJE-Bridge[5]? <-----

Your description of the history of terminal support in MTS is mostly correct except that the 2703 wasn't replaced by any of the others, it coexisted with them until the end. I'm not an expert on BITNET by a long shot and BITNET was never more than a bump on the side of MTS. I know we supported EMail via BITNET but I can't recall what other services, if any, were supported over BITNET. What do you want to use BITNET for? Are there any hosts out there still using it?

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7.) ASMH is not available due to licensing. More than half the
system is written in Plus[1]. Is it possible to recompile only the
Plus-based portions, plugging in the already-assembled (and/or
manually patched) ASMH portions after the fact? Or is ASMH still
required for the existing build process, absent some heavy
modifications to the build scripts? (Not that I'm capable of any
meaningful modifications, as my programming skills are nascent.)

You should be able to rebuild any module (Plus, ASMH, GOM, or whatever) without affecting any other module. Neither the GOM nor the Plus compiler depends on ASMH.

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Thank you for for taking time to respond to these questions.