The only concern with the SM-420 is the bolt holes in the mounting ears. SM-420 mounting ears
The Chevy V-8 truck bellhousing from '55 up (not including the ones around '62 with the hydraulic clutch) looks like this: \'55 up truck V8 bellhousing
I ran a '69 350 in my '49 half ton with this bellhousing. I had also used a '54 crossmember which bolts to this bellhousing in the '49 frame.
Notice the upper mounting holes are tapped while the lower ones are drilled to match the SM-420.
I see these bellhousings on ebay frequently listed as Corvette items. Easiest thing to spot is the reinforcing ribs above the upper trans mounting holes.