You have to replace the upper and lower as a pair, the ports are different then the stocker so they're not interchangeable. To swap the throttle body you have to take it apart and put the mustang linkage on it. It's doable but much easier to just buy an aftermarket throttle body. Yes to see the most from it the throttle body and spacer should be the se size as the opening. You should swap the MAF as well, the stocker is only like 52mm or something. The stock one off a 94/95 5.0 is the cheapest option, bolts right in and is a 73mm.so im getting ready to the the explorer intake swap and have a few questions. Should I also replace the lower intake with the top? Does the throttle body from the Explorer easily swap into the Mustang? Im not sure but shouldn't the size of the throttle body and EGR spacer be equal to the manifold? Any additional thoughts would be awesome