Considering running/driving 4.6L cars are cheaper than running/driving V8 Mustang IIs and fox-bodies at this point... No.
I kid you not, I can find running/driving '96-98 4.6L cars in decent for under $3000 all day on Craigslist, but a running and driving 5.0 Mustang II or Fox usually brings twice that unless it's a total basket-case.
If you REALLY want to do a 3.8-to-4.6 swap, you can. You might even be able to scrounge up the parts for just a bit under the price of buying a running and driving 4.6 car, but that's an awful lot of labor to put out just to save a little bit of money, and to be honest, the engine-swapped car will be worth even less when finished than a factory V8 car would have been.