Does anyone know which pattern # was correct for the camaro?
It would be interesting to confirm whether or not each Camaro master cylinder part number has a discrete foundry pattern number particular to it, for example D7 for manual disc and D14 for power drum. I don't know if that information exists anywhere.
In any event, there are at a minimum 4 possibilities; manual drum, power drum, manual disc, and power disc. The master cylinders for power drum or power disc brakes would have bleeders incorporated into the master cylinder due to the master cylinder being mounted at an angle; whereas the manual drum and manual disc brake master cylinders do not have bleeders since they mount horizontally.
In addition, the master cylinder bores are different between drum and disc brake cars.
One other difference - quoting a previous post from JohnZ: "ALL factory drum brake master cylinders have RPV's (Residual Pressure Valves) behind the seats in the outlets, as do the rear outlets on disc/drum master cylinders. The RPV's maintain 10psi at the wheel cylinders to overcome the initial tension of the shoe pullback springs and get the shoes out close to the drum surface to minimize pedal travel when depressing the pedal."
Also, see the following: http://www.camaros.org/suspen.shtml#Brakes