'71 FWD caddy 500? Didn't know there was such an animal out there.
IF the Caddy 500 is in a RWD boat, you can pull the engine, trans, driveshaft and rear (the rear is W-I-D-E though).
There are a few bucketheads that have used the Caddy 500 and they LOVE it because of the stump pulling torque of the engine.
It doesn't like to go over something like 5000 rpm, but when you have gobs of torque who really cares about high rpm anyway?
There are a couple of EXCELLENT Cad 500 forums out there and they can tell you everything you need to know about that engine.
I still want one, just haven't found the 500 yet. Two 425s and one 472, but no 500 yet. YET.
(edit)
It seems that the Eldorado was FWD... I had no idea. Learn something new everyday.