This has been covered on the RSR in the past, but not definitively. Leaving this information here for the next poor fellow who is in this situation -- this is what you might call a Comedy of Errors.
I had to cut an SCCA weekend short because my rear master cylinder was leaking. I ordered all 3 MC replacements from Spring Mountain, plus replacement biasing hardware.
Problem Zero: My PR6, chassis #003, has very different master cylinders from the current factory parts. In particular, the pushrods for the masters are VERY different in length. No worries, I wanted to move the pedals anyway. They were in the closest of three positions, and I wanted the far position.
Problem One: It's impossible to take the master cylinders out through the inspection/service holes in the crashbox, BECAUSE they're bolted in and then the crashbox was riveted together. I am not making this up. So I had to drill all the rivets out of the crashbox.
Problem Two: The pivot beam for the pedals is too long to remove from the bracket, so the pedal box has to be removed. It's riveted in.
Problem Three: The brake bias adjuster cable passes in front of the clutch pedal. So the clutch MUST be adjusted to sit farther away from the driver than the brake pedal. Otherwise when you hit the brakes hard the cable will bear on the clutch pedal and adjust the bias for you, on the fly. When I removed everything I saw that the cable had worn the clutch pedal arm shiny.
Problem Four: There's no combination of adjustments that makes the current Radical MCs fit, so we re-used the original pushrods. At that point you might as well do what Robert at Radical Canada advised me in the first place, which is to rebuild the MCs I already had.
Problem Five: The original pedal carrier was bare of paint from where it was mounted to the floor. It must have been painted after installation. After 16 years it looked TERRIBLE but it was easy to refinish.
Problem Six: The PR6 is riveted together with what looks like metric rivets. 3/16th is the closest equivalent but if you want the 3/4-inch rivet head you'll need to plan ahead, as that's not commonly available at a big box hardware store.
Problem 6.5: Since these are blind rivets, once you drill them out they are going to rattle around in your frame tubing until the end of time.
So my recommendation to PR6 and Prosport owners who have a crashbox -- that's not everybody, from what I've read -- is to evaluate your master cylinders and consider making a winter plan to remove what was for me a total of 56 rivets and get everything up to snuff before re-riveting. At the very least you'll need the pushrods from your existing cylinders, as both the Radical and aftermarket choices are TOO LONG and don't have enough threading. And this is a good time to see if you want to move your pedals! In the end we went back to the short pedal position because the existing pushrods didn't have enough thread on them to accept the pedals in the "tall" position.
In the meantime, take a look at how your bias adjuster interacts with your clutch pedal.
Oh, and like Columbo, I have ONE LAST THING. My crashbox was installed -- and this is the factory install, unless the person who redid it was SUPER CAREFUL and lined up every rivet head with the original impression -- in such a way as to crimp my right rear brake line. Sure enough, my right rear disc looks a lot fresher than the left rear. So that's worth checking the next time you have the nose off.
