Transmission debacle

You can damage the sprag in either a 727 or 904. It's just that a 727 can explode. I've never seen a 904 come apart like a 727.

But also, make sure that neither transmission takes a lock-up converter, which would limit your converter and valve body options. In a lock-up trans, the input shaft tip is machined about 3/4". In a 904, the lock-up version may also have a 2.74 low gear, which you would be unnecessary with a high torque stroker.