It should swap out but I don't believe you gain anything over the stock GT shifter, in fact I think they're the same parts. I would upgrade to an MGW if you're going to go to the trouble of swapping it.
Is there a particular reason you wan to swap (same for same), or just looking for nicer shift knob? If part-2...just swap knobs (like other posts state).
If it were my car, Id get an MGW setup for stock threads, and put that black Boss knob on there. Especially if you've already got that Boss shifter for parts. Best looking and best functioning