Explorer rear has the 8.8 but axle width is wrong. Honestly though that can wait. Not sure what your budget is, but if you are building a 400hp car chassis prep will be key. Maximum motorsports full length sub frames, tubular a arms, and k member brace are going to be key. Your existing k...
Having done the swap i would beg to differ. If it solves an existing SD issue you either had a bad ecu, wiring, or vacuum lines. All of which can be solved much more easily with some simple diagnostics and 20 dollars in supplies.
Even a high idle is a sign of a leak or improper adjustment. Go through the base idle reset procedure and go from there. There's a lengthy idle sticky in the tech forum that will go into much more detail if your problem persists.
Do yourself a favor and replace your vacuum lines and rubber fittings before you start, including the rubber grommet going to the brake booster. These are notorious for cracking and you'll be chasing a hanging idle forever.