Mustang cars are uni-bodies. There is NO frame, so they have to be reinforced with sub-frame members to keep them from "Torsioning" the body.

Ranger pickups are as small as you can get, can be made very light, are infinitely modifiable. THEY HAVE A FRAME...

The beauty of a frame is that it IS THE major structural member and lends its stiffness to whatever is mounted to it. It also means you can mount whatever you want TO the frame with a minimum of worry about how to make the overall POWERTRAIN fit without the structure being weakened in a critical way...

AND - it has been demonstrated that a Ranger frame will even handle the output of big-block ford engines.

It's the ideal hotrod chassis.