The master cylinder is a 15/16".
Regarding pedal ratio, my brake pedal actually has a higher ratio than stock. I drilled a hole above the original pushrod hole to increase the leverage. The A body booster and linkage are all on the engine side as opposed to the B body setup where the booster bolts to the firewall and the reduction linkage is under the dash.
The increase in ratio at the pedal is minimized by the reduction linkage but in short, the ratio is still greater than stock, even if only by a small amount.