It is used on street rods because of the width and it is a drop center 8"type rear. Lots of custom gears available for it. It looks good. Tho, now it is getting hard to find.
The Mustang rear loader didn't get popular with the street rod people because it is hard to set up, it's ugly and sometimes a bit pricy on initial cost.
Now street rod builders are using the S-Truck rears. CHEAP, and gears and parts are everywhere . Also rears from early 90's T-bird/Cougar Fords are good if you want a simple independant rear suspension. They remove from the donor car with six bolts and are very adaptable to older frames. They give you disc brakes, Independant rear suspension (good ride). Tho the gears are a bit non performance. Aftermkt gears are available. They are also a good looking setup.