Using ADJMEM as described by you seems to solve the memory usage problems, thanks!
The addition of MCGA hardware support, even if mostly for its lack of support for EGA mode 0xD, is an interesting case. So is the ability to take advantage of smoother fading; I think the latter should also be possible with the VGA while using EGA mode 0xD.
Since ModID supports Wolf3D's VGAGRAPH files in addition to CGAGRAPH and EGAGRAPH, there was a point in which someone known as furan was experimenting with upgraded VGA graphics, using "cksrcmod" as a base. The work was not finished, but here's a K:M thread: https://www.keenmodding.org/viewtopic.php?t=1940
One bit of thought I've had, is if a Tandy adaptation can be made - at least for the song "Too Hot To Handle" - when it comes to Catacomb 3-D. I don't even know if it's possible to get a port of it to work with acceptable frame rate on the Tandy 1000. BSzili used Reflection Keen (ReflectionHLE) as a base for Amiga ports of Keen Dreams and the 3D Catacomb games. He also ported Keen Dreams and Catacomb 3-D to the Amiga CD32.
Ignoring the frame rate, I expect porting Catacomb 3-D to be at least as challenging as porting Keen 4-6's Star Wars styled scrolling texts.
I'll finish with a few more comments specific to the TANDY and MCGA builds:
- One interesting side-effect of the port is that like the CGA builds, the Tandy and MCGA builds seem to ignore the sprite's shifts field. This leads to smoother horizontal movement of the Dopefish, compared to the original EGA versions.
- It looks like there's a problem with setting the viewport camera position around the bottom edge of a map, or alternatively the bottom of an area bounded by a scroll bar. The camera will briefly pan when you enter, e.g., level 6 or 18. Same holds when entering the first house in level 15. This is further reproduced by pausing or showing level stats and then returning to the game.
- There are multiple rows of pixels around the bottom of the screen which aren't drawn at all in Tandy and MCGA modes. They're left black-colored. The menu, help screens and ending sequence look ok.