how to swap 96 3.8 to 5.0 carb.

Well, first off....I might be totally wrong but I thought there was some laws that don't allow you to run a Carb engine if the vehicle ran an EFI to be street legal. But if you can or still want to, you will have to get a correct K-member from a 94-95 GT, GT driveshaft and it makes sense to swap in a 8.8" rearend as well. Any T5 should work, but you may need to make some minor modifications, depending the exact tranny. You are also going to want to upgrade the radiator.

Honestly, if you are thinking about a carb engine you might as well look for a EFI 5.0 swap or even 4.6. To make it worth it, I'd have to go 351 atleast on a carb to make it worth it. But whatever works best for you.

Things you'll need:
94-95 V8 K-member
8.8 rear end (86-98 are the same, can reuse axles from 7.5 rear)
V8 accessory brackets (could use Fox brackets, but it's a tight fit between the brackets and radiator)
V8 gauge cluster (will want for the correct speedometer and tachometer)
V8 transmission (can use Fox, but will need driveshaft spacer for the slip yoke to fully engage the output shaft. Steeda sells one)
Larger fuel pump
Fuel lines

That's all I can think of, off the top of my head. You might be best off finding a wrecked 94-95 to use as a parts car, and parting out what you don't use to make back some of the initial purchase. The member Chythar in 94-95 is currently working on a V6 to V8 swap himself from a wrecked Cobra, so he might be able to give you some advice. There's a few guys in 94-95 Tech that have gone carb that could probably help as well.