Buy a good running pullout from a 96-99 Explorer, swap out the cam with a good GT cam, swap the springs with some new TFS springs, drop it in and run that.
$2k is enough for a basic rebuild and the google will tell you that pretty much any motor can go into a mustang.
2000 Mustang GT Steeda #0048 34k miles. 99 Cobra 4V swapped, FTBR IRS swapped, exhaust, tuned by James Gordon.
Just because I give you advice, doesn't mean I know more than you. Its just means I've done more stupid ****.