Seems to me Buick V8s were sold to RangeRover/LandRover. Perhaps a bellhousing from Range/LandRover could also be used.
3.08 gears are not desireable in a wheeler, however they should work fairly well with a sm 4.20 with the 7.05:1 first gear. If I were building it, I would look into using an NV4500 5 speed, and lower gears. How low the gears are depends more on Tire size.
28 inch tires 3.73 gears
31 inch tires 4.11 gears
35 inch tires 4.56 gears
