If you're going to swap in a mod motor use one from a 2005 through 2010 Mustang
GT. You will need to get the K-member from a 1996 through 2004 GT. It's preferable that you source an aftermarket K-member for weight savings. The V6 K-member will not accept the mounts for the V8 mod motor. Remember that you will have to get the wiring, EEC-V, V8 front suspension, fuel lines, transmission, and rear axle replaced for ones used in V8 models. The V6 has a weak 7.5 rear axle where as GTs and Cobras use an 8.8. There's a bunch of little things that need to be swapped, too, so, you'll want a wrecked donor car to scavenge from. Do it yourself. Don't pay a shop to do it and you'll save a bunch of money on that alone.