Heavy-duty front disc brakes ... so it seems we know who made the most powerful muscle cars in the '60s.

Slotting a larger 428 ci V8 under the hood, Royal also modified the front and rear suspension ... arguably one of the prettiest muscle cars to emerge from the '60s, as well as one of the fastest.

One of the muscle cars sitting in the Brothers restoration shop is this 1970 Plymouth Superbird, which was the first muscle ...