1968 Big Block

Truck mounts don't work. You need the factory 3 piece Mustang mounts for what you want to do. Although big block Stangs are awesome performers, to get the performance you'd get with a 390, you can get it with a stroker 5.0 ( 331 or 347) or a 351W today, without all the hassles of finding the swap parts to do a big block. It's not that easy to swap in a big block, you'll also need to swap transmissions if you now have an automatic, the trans crossmember is different, a spring upgrade to handle the weight, plus the big block cars also had beefed up shock towers. Not to mention you'll also need to upgrade to a 9" rear if you haven't already.