I totaly agree with Dave Severson, You should go with a big block.
I grew up in Las Vegas thru the 60's and 70's used to go to the desert races/hill climes/ mud boggs all the time. Alot of my friends used to compete or take part in these races. It was always the big blocks that came out on top. It takes alot of torque to turn 44's over in mud or on a big hill. A small block has to rev way up to get high number HP. Lets face it the first time that the engine boggs or miss fires it's sunk, It won't have enough torque at low RPM's to turn those big tires over in the mud. Build a Big Block and set it up for low RPM's for pulling. That Caddy motor would be a good choice, since you all ready have it. Just the way I see it.

~ Vegas ~