I was at a Fiero club convention some years ago, and those guys had all kinds of engine swaps, SB chevy, Buick 3.8 supercharged Ultra engine, etc. One guy had a Chevy 3.4 OHC V6 in one , with a turbocharger on it ( that one would really haul!). One guy had a BB 454 Chevy in one. Way too big and heavy I would think.
The one with the Buick had the whole Buick drive train bolted in place of the Pont drive.
With all the engines that are around, the Caddy 4.xx family is the last one I would pick, even though the 4.9 is supposed to be the better of the three.