Any V 8 will need the 22 Gal cell to be close to competitive . The early Stang could be good with a decent small block Ford or Chev, and top loader. Most of the parts can be bought for a fair price . Use the 17 in wheels and 13 in brakes front and Explorer 12 in on the rear . Reduce the rear spring rates and add an adjustable track bar. The front needs the new track rods and the Shelby upper ball joint spacer kit. Use some 2x4 tube to run under the car and link the front to the rear and be the lower cage mounts. Link the cage to the upper front towers of course and weld the crap out of the lower frame sections to the frame tie tubes. Adding the convertible front frame panels could be a good move .
These cars are really weak stock and need the front tied to the rear pretty well . They can be really fun to drive and reasonably durable.
My Recently sold Ranger is very similar or better numbers than the Stang with much better balance and 22 gals of fuel. Good numbers for a Contender overall. 250 HP or more,22 gals, sub 3000# race ready . Lots of tire .