The GMM Ripshift and Billet Products Australia shifters are direct bolt-ins for the GTO. A F-Body shifter can be made to work by changing the small "cup" on the end of the shift-rail that receives the ball on the end of the shifter; some other creative measures may also be needed depending upon shifter brand.
__________________ Mike - Impala herder with a stray Goat.
2004 PBM/M6 - 1 of a bunch - Stuff's been done.
1966 Nova - 6.0/TKO600 in the works.
If you disassemble the stock LS1 shifter, you can enlarge the opening on the mounting plate toward the back by about 3/4 of an inch. You need to then drill and tap the holes for the shifter to mount back on the plate, and bolt it back together.
I should've gotten pics of it when I did it, but I didn't have a clean set of hands.
Then again, you could cut the hell out of the trans tunnel to have the stock GTO shifter fit, but why?