Yeah, you can get a crate LS6 in a couple of different versions, here's one...
http://www.crateenginedepot.com/stor...268-P10C0.aspx
There are also lots of re-sellers of used LS6's harvested from Camaro's, FB's, Vettes and GTO's that are pulled out of ditches shiny-side-down. Just do a search on eBay and you should see several of them.
But as far as I know they don't make a specific "Pontiac" version of this GM engine in crate form. You'd have to get those plastic "GTO" covers or an actual GTO LS6 from a wrecked car or off eBay or something.
This wouldn't be a bolt-in swap by any means and could be a little tricky, but definitely could be done.
There are some excellent forums that would be a lot of help at
http://www.ls1tech.com/forums/ - many folks there have swapped LS1-LS7 engines into vintage cars, including A-bodies (mainly Chevelles).
I looked pretty hard at this option and did some research, and came to the conclusion that even if you were able to do this as cheaply as possible, it would still cost you more and be way more trouble than a seriously bad-ass professionally built and tricked out 455.
And you'd retain the respect of your Pontiac colleagues as well, which is of course the most important of all.
Chris