Hard to beat the aftermarket support of the Fox platform...as long as you like the looks of the Fairmont. I like the idea of an American M5 also, though I'd go the other way and transplant a LS and 6 speed into a nice 5 series.
Martin Pond has a very well built 2 door and wagon that can be drivin daily and tracked all weekend. He's completely lost his mind and is now building a Ford Durango...yes it exists, look it up.
For the amount of money and time you'll have invested, have you looked at mid 60's Falcon or Fairlane wagons? A lot of what you're planning can be done to the earlier cars and.....not look like a fairmont.
