In 1969, my Brother and I converted a '58 Microbus to a solid rear axle, ripped out the interior and put in a 6-71 Supercharged Big Block Chevy. Ducted the exhaust out of the top near the corners (where there are not windows...) and mounted the radiator just under the roof. NACA ducted the intakes (also roof mounted) for both the radiator and the engine. Boxed the the works to keep the heat down in the interior. From the outside, it was just another ratty Vdub with painted out side windows. I don't think we paid more than $40 for it as the engine had been cooked.
Have to admit, it really did not handle very well. But then again, ask me if we cared...