I don't think the 428 would be a good swap for a fox. Please don't get me wrong. I absolutely love the 428(see sig). Also depends if it is a cobra jet, if not it was probably lifted from a truck or wagon. You would be better off putting a stroked 351 in there IMO. The potential weight of a 351, ease of finding parts and cheaper, ability to bolt it in without too much work really make it the ideal swap. Leave the FE for the classics. FEs also have heat issues so there are a lot of things that are tricky with them and don't have 30 years of refinement to back them up. Again, I do love the FEs but are probably not best suited for your street fox. A CJ will probably will tweak your T top pretty easy in stock form too. Definately get some subframes and possibly a cage.
Kevin