The pipe diameter is different between the 3.7 and 5.0, so no axleback exhaust from a 5.0 is going to bolt up to a 3.7, UNLESS you cut the pipe part from the donor 3.7 axleback (rearward muffler side), do the same on the 5.0 muffler, then weld the 3.7 onto the 5.0 axleback.
Is it worth it for performance? No! Is it worth it for sound? Maybe. I purchased a set of GT500 axleback mufflers and did the exchange to my 3.7. The sound is nice, not loud. Did I get any performance gains? Not that I'd feel in the seat of my pants. As to a GT axleback on a 3.7? May not be worth the fee a muffler shop charges you to do the cut and welding.
Axleback mufflers of ANY type will not net you any HP gains. They are for sound change only. A set of shorties, longtube headers, and mid-pipes are what would be needed to gain HP in the erea of exhaust, but will also require a change in the intake, and of course a tuner/tune.
It is better to keep your mouth closed and let people think you are a fool than to open it and remove all doubt.