well being that the grand prix is a front wheel drive vehicle and the LS2 is predominantly rear wheel, good luck with that. There is a guy over on LS1tech who is swapping in an LS2, IIRC, into a 308 and I believe he was creating a custom bell housing in order to use the 4T65. Not much progress has come along since last year tho.

Like GTP 98 said tho, your best bet would be to do an LS4 swap, especially being that the 05-08 Grand Prix had them as an option.