What wheel cylinders?

I've got a 67 Valiant with manual 73 and up front discs and 8.75 11x2 rear drums. I just swapped the orig. master cylinder to a 73 and up power master cylinder. What rear wheel cylinders do I need? It has the original 3461776 cylinders right now. The rears are locking before the fronts. Im also running the stock distrubution block, untouched.