Actually the 3L TB would take quite a lot of modification to work. It has nothing to do with the manifold used. The machining is different and it's 180 out.
Modifying a 4.6L 65mm (or 70mm aftermarket) is a much easier task and a better route with the larger 3L engine.
The 3L UIM also would require some tweaking to use, plus the big hood clearance issues...
The 3L LIM needs modification to use as well.
Now dropping in a complete 3L (pan through upper) and you would still need to use a 2.5L TB setup and the previously mentioned hood clearance problems...
