Ive heard that a drum prop on a disc set up will actually make the disc rear a little quicker and tighter to react when you push the pedal

If you switch from a drum to disc rear without changing the prop valve you'll end with too much braking at the back and the rear will lock up. The adjustable valve goes in line with the rear brakes and reduces the pressure to the disc rear to allow the front brakes to work properly without rear end lockup.

Best 3rd gen braking setup is 1LE/LS1/C4/C5/CTS fronts with an LS1 rear. If you go from a 3rd gen disc/drum setup to one of these the braking increase will be hugely noticeable. IMO the stock 3rd gen brakes are crap compared to what you can create. I had a 91 with 1LE/G92 and it paled in comparison to Shel's LS1/LS1 setup.

the only reason I want to swap the rears is because i already have to stock disc setup. its just off the car. I would change the rears eventually but money is an issue right now and i already have the parts to swap to LS1 fronts and stock disc rears.

If you have LS1 fronts and 3rd gen disc rear you may be all right with the 3rd gen disc/drum prop valve as both ends are getting better braking. You'll know as soon as you drive it and brake hard. As long as you can't lock the rear before the front then you're fine.

Just a question, what is the difference between a prop valve off a J65 equipped car and a 1LE car?

NEED HELP!!

I have almost got my from LS1 swap done, and while trying to put the caliper and caliper carrier on over the rotor, there is a huge gap between spindle and the carrier bolt holes. I have the complete setup that came off the LS1 car, but why is there such a big gap? how do I fix this? or are there 2 different types of rotors?

Brent