What brakes do you have on the front? If there not matching I dont think a prop valve will solve your probs
I tried to get one from a the dealer and no go, so used is the only option AFIK
I do think it would be a good thing for some vendors to look into
I have the stock drum prop valve with 11" fronts and vented rears and the rears never lock up before the fronts do. Only if I slam the brakes hard then all 4 wheels lock up. In normal driving the brakes feel great and it'll put my passengers thru the windshield.
I'm using the vented rear disc/11" front brake master cylinder. The 11" vented rear setup and master cylinder are off a '90 Daytona, the 11" front setup is off a 92 Daytona. New pads and rotors all the way around.
another thing you can do is like I did and use aggressive pads up front and stockish pads in the rear to help(since I'm using a drum prop valve with full R/T brakes, but I also have wider tires then most)