"heavier truck" question...........

I don't think you're going to find an SAE bellhousing for a small block, typically bigger trucks with a small block would have had a Clark 5 speed or an NP435. Big block trucks did use SAE bell housings but they were massive with rear motor mounts built into them.
If you want a 5 speed the NV 4500 would be a bolt in deal, they were stock from 94 up. Those Fuller transmissions are way overkill for a small block but would be just right behind a Cummins hint hint....