Changing rears to 3.7 may not be enough. Maybe 4.11's-4.30's to get the rpm's up 25%. Also, smaller diameter tire?
what about a truck 2 speed rear?
Maybe sprint car style quick change?
Somebody was making a ford 9" center section interchangeable with the dana. I think he had a machine shop in CA, made remote
oil filter brackets for cobra's, and owned csx3020 at one time. If you switch to a 9", swapping out the rear gears I think would be a lot easier.