I thought a different master cylinder was needed if you swap 73mm calipers onto a stock 5.0, but it's not mentioned. The SSBC upgrade kits you used to sell had a new mc for this reason. Can I keep my factory '92 5.0 mc with this kit?
Swapping to a different master cylinder isn't required with this kit. The reason the SSBC kits included one is because 87+ master cylinders do have a smaller output capacity, and with their rear disc conversions, that can cause a spongy pedal. Having said that, this kit alone does not require a master cylinder swap. Pedal effort will still be nice and firm.