i am looking into doing the swap in the front and later in the rear

What prop valve should i use or is there a direct fit adjustable?

will my 20 slot 16" formula rims fit?

what master cylinder and brake booster should i choose for maximum performance?

You are referring to the 91 RS I presume.

First all of your questions can pretty much be answered with searches but it does take some piecing together.

I'm not a brake expert for these cars so all I can do is share my experience and opinions. My car is an 89 IROC with the PBR rear discs so nothing was necessary to change other than the front brakes. Using that as a baseline the MC PV from an 89 IROC should work once you get to the rear disc phase. You could check to see if the MC in mine is the same as yours you may not even have to change the master. As far as LS front/drum rear your pv will probably work as is for now. The pv won't really come into play until you go with the rear disc.

Never seen a direct fit adjustable but it wasn't necessary for me.

I'm running stock 89 IROC 16" wheels. Don't know about Firebirds but there's a sticky thread about brake/wheel fitment. Check it out.

But search search search. It is worth it to get the information you need. The LS brake swap is well worth the effort IMO. And quite frankly it isn't too difficult especially if you contact Scott at bigbrakeupgrade.com and get a set ready to go.

This swap will be done to my current thid gen my 89 TTop Formula (1991 350TPI(L98) swapped) car Originally Vin "E" 350 TBI
. It has stock isngle piston calipers in the front and stock drums in the rear
it is getting the ls1 in the front for now then when i build a new axel(winter?) it will get some gears and disc posi ls1 style of course and line lock for the front

I have Pontiac 16" 20 slot rims will they fit correctly?

thanks
jake

Fronts:
-Stock MC and booster will work just fine with LS1 front brakes. The advantage of swapping to 4th gen style is they are more compact, so you can clean up the engine bay a little.

Rears:
-Stock disc/drum PV will be just fine now, and when you swap over to LS1 rear brakes IF you are a street driven car that sees little to no track time. If your car will be seeing marginal, moderate, or greater amounts of track time, a 1LE disc/disc PV or an adjustable would be required. Wilwood makes an adjustable PV that fits our cars, I beleive summit sells it

The 16 inch 20 slot formula wheels will fit. Source? I fitted one on my own car. Was gonna do the swap on my 84 and got the 16s for better tires/performance, before changed plans with the car, the 84 is now a parts car, and I'll use my 88 as the basis for the build mainly because it is rot free. Here are pics below, I'm moving everything over to the 88 over the winter.





I spun the wheel and it clears, no dragging or rubbing.