i'm not too sure why you'd want to, except to be different. the 3800 is a great starting point for any performance build. but if you really want to do something bigger and different you could swap to a caddy 4.9 v-8 (not recomended, it'* a great motor but it'* not better than the 3800)the northstar feasible swap.
using parts from this kit you could drop a small block chevy transversly and retain FWD. expensive, but ultimatly cool.
check out some of the engine swaps these guys have done. many of the swaps they've done can easily be done in a bonnie without too many major tweaks to their layouts.
whatever you choose, make sure to take lots of pictures... and definatly bring your wallet.