@OneSwitch I just came across your thread on Gorf here. Gorf was one of my grail type games that I was never able to get to run right. It never made sense as to why it was so slow, but seemed to slow way down on the Galaxian level when there was a lot of sound. I copied your plan with mame2010 and lo and behold there she goes! I have it running on my Mad Planets cab (build thread posted last year), so I have the trigger stick and everything.
From what I remember of the actual game, it was a little bit sticky. You might think you still have a performance issue but I think the game was never all that smooth. The mame2010 emulation feels totally accurate.
So thank you for figuring that out, it checks a huge box for my collection!
Resurrecting an old topic, but just a note that if you update RetroPie-Setup to version 4.3.8 or later and reinstall AGS, MIDI playback should now work correctly - no need to install the GUS patches manually. AGS content will also automatically appear in EmulationStation without the need to manually edit any files. I've removed the obsolete instructions from the RetroPie wiki.