sooo jealous, I'll give you $450
Personal opinion, depends on how original you want to keep it and how new you want to go with the driveline. Also depends on what you want to use this for.
If you want to keep it fairly stock and horsepower, etc isn't a huge concern but you want it to run nicely the Buick 350 may not be a bad idea. Since it was the original motor, all the motor mounts, exhaust, rest of the driveline, accessories, etc will still bolt up without a problem and you can just refresh it and add fuel injection. That's do-able but its roughly 3500 for the FI kit and when you break down in the middle of nowhere Buick 350 parts may not be something everyone keeps on the shelves. Also the rest of the driveline wasn't setup to run 75 down the freeway so gearing etc may come into play.
Lots of LS/5.3 Swap info and Universal support. Not a bad swap if you don't mind a chevy driveline. Being that its a Buick 350 I guess it kind of already is isn't it?
Parts down the road would be cheaper and easier to find, could probably build the whole setup for less than the Buick fuel injection Kit.
but no, I can see it in your eyes, you want to keep it Mopar so you should definitely do a Hemi swap
You would probably have to do a little more fab work but there's definitely some support out there. Pull the whole driveline out of a wrecked Ram and you'd be set. Make sure it's a early 00's so there's no MDS and don't do what I did, just buy the standalone plug n play harness and save yourself the time and headache