So, I've been trying to get the alpha/betas included in the Marathon Trilogy CD working in SheepShaver. For awhile, only the "macworld sf - jan 94" alpha would work & the other 2 builds "first non-orthogonal - may 94" & "feeling the noise - june 94" would crash SheepShaver immediately after opening them. But, if you check match the preferences show below, those 2 betas now work.
And here are screenshots from the starting location from those 2 betas:
I'm running System 7.5.5 in the latest build of SheepShaver for Mac OS X.
Oh & 1 more little tidbit of information: if you open up "marathon.alpha.fat" from the "feeling the noise - june 94" beta in ResEdit, there's a folder icon that wasn't used for the final version of the game