my 2-cents..
when properly tuned, turbo cars are a LOT of fun, more than a V8 IMO, however, they can be very frustrating, especially during the learning curve - as you learn how it all works. I've had both V8 powered Monte's and turbo V6 Regals. Based on my experience, the turbo cars were more fun, but the V8 cars were MUCH less trouble. What you are proposing is a little different however. I looked into putting an LS1 into a Monte SS a while back, and from what I've read, an LS engine will *not* just drop into a G-body, you will have to modify the cross member and there are a few other issues to sort out. If you have the $$$ to actually do the LS swap then you might as well spend the money on rebuilding and updating the engine to an '86/'87 Buick setup.
Rob