DesertStrike86,
I did a '96 Explorer drive train swap in my 1966 Ranchero. Your '65 Mustang will be a couple inches narrower, as the '66 Ranchero is the same size as a '67 Mustang. If you want to keep the Explorer serpentine system, which btw works great, you will likely need to make some motor mount adapters to slide the engine forward about 2". This is so the AC, pwr steering pump etc clear the shock towers. If you are cutting out the shock towers for a modern front suspension, obviously not necessary.
The nice part about this is you can put the explorer computer in the firewall just under the radio where it would be located on the Explorer. Less wiring to mess with. Moving the engine forward also allows for easy access to the computer. Even in an old Mustang things are going to get tight...
I strongly suggest you get an aftermarket Mustang fuel tank that is already setup for an in tank pump. This will save you from having to cut and modify your tank...Mustang guys have it so easy anymore
. I tired several iterations of inline pumps and in the summer and at Colorado's altitude they all tended to overheat similar to vapor lock. consider that nearly all modern cars with EFI use in take pumps.
Another suggestion is to dump the stock Explorer exhaust manifolds for some from a 93 Mustang...I used stock ones, there are other options as there are tons of aftermarket options for the 90-93 Mustangs.
I did not end up using the 8.8 out of the Explorer, but good option. Let me know how it fits...
I ended up modifying a 9" and had it modified to fit the Explorer brakes...btw, I went with '78 Granada front disc brakes but there are lots of aftermarket options here too. Notice the Explorer disk brake booster as well. The brake power booster is from a Fox body 4 cyl...pedals are modified.
Here are a few pictures of the Explorer swap in my '66 Ranchero...
Peace & Enjoy,