That’s VERY nice. The wheelbase matches perfectly (as far as I can tell).
You ought to be able to fit just about any manual under that. The beer-tap shift knob might gash the headliner though :). And while you might not be able to manage fitting a Cummins in there, the Duramax will probably work ok. Not sure how the Powerstroke would work, as it’s pretty tall.
And yeah, whoever did that conversion spent some time to do it right. Everything is very nicely proportioned and spaced right.