New 4.6 to old 4.6
 

Can I take an old 4.6 (96 model) and swap if for my 08 4.6?

Kinda doubtful. BUT, anything can be done with enough money to throw at it.

I'm not completely sure but I think that the 08' is a 3 valve engine. and most likely the 96' is a 2 valve engine.

Well also, the 96' is "mostlikely" not a over head cam engine ( aka modular), but still is a push rod engine that has a central internal cam.

Like mentioned earlier....with enough money...and time....it could be done.

Nope, they are both OHC 2V engines. The 96 is non-PI, the 08 is PI. They will physically swap but you will have manifold and other component issues, and it will have considerably less power.

If it's a 96 engine, it's probably out of a car. Trucks and vans didn't get it till 97.