AZ, The main external diff between BB and SB toploaders is the size of the input/output splines; along with internal changes, the BB toploaders have a higher torque capacity. The cases may be the same or very similar. Check with David Kee.
I was told that the truck toploaders have a low-low first gear (grandma). They could no doubt be used behind a 428, but you might want to add a drawbar so you could plow or pull stumps with it (
).
The small toploader can/has been used behind 428s, and would do okay for mild street use, as long as the tires didn't hook up.
Comments, guys?