Both engines average 550 in weight. The SBC is slightly narrower and 3 inches shorter front to rear. with air cleaners being different, the SBC usually comes out 3 inches shorter with comparable set ups. I shoved in a 305 SBC in an '81 D-50 Mini Ram using stock manifolds etc. I had an advantage of it being converted to a 4X4 from the dealership (wasn't available for that year from factory). I had plenty of room to fit everything and revamp exhaust and stuff. I did manage to get it all tucked in neatly as if it was a 2X4 set up. Don't over power it, the rear end is pretty tough, just not tough enough to handle a warmed over engine.