The 4.6L is a WIDE engine.
I've seen it done. It involved cutting out the front shock towers, different suspention, many other custom modifications, donar car and a lot of skill and patience. You really need to know what you're doing.
only an experienced mechanic with fabrication/ modification experience can perform this job. anything can be put into something else if you have the know how, and the tools. i've seen a BOSS 302 installed in a 69 VOLKSWAGEN. it all depends on what you're capable of. as far as switching it over, you're going to have to modify the intake because a 67 doesn't have a computer where as the newer mustang does to operate the fuel injection. and then you also have to modify the motor mounts, tranny, blah, blah, blah.... good luck. you're gonna need it