First, since you are mixing/matching parts, make sure your crank is drilled for a manual transmission. Most are, but if not, you won't be able to fit the input shaft into the back of the crank.
Stock Pontiac disc is 10.4", but the 10.5" is what you will find/use when using the factory cast iron flywheel. If you use an aftermarket steel flywheel, like Hays, they are drilled for both the 10.5" and 11" pressure plate/disc set-up.
Make sure you get the correct flywheel-to-crank bolts. Use the incorrect ones, and the heads of the bolts are too thick and will hit the center hub of the clutch disc - ask me how I know. LOL There is a set for the automatic flywheel and one for the standard trans flywheel.
You want to make sure you get the correct length throw-out bearing. There are three sizes, long, short, and intermediate. They also have different faces to match whatever style of "fingers" are used in the pressure plate. McCleod sells an 11" kit with the wrong length throw-out bearing for the Pontiac. They may have corrected this in the 10 years since I had purchased my kit. Had to shell out more money to get the correct length, so the "kit" was not so complete and I paid for the throw out bearing which was incorrect. Of course figured this out after the trans was installed and the clutch simply would not disengage no matter how I adjusted the linkage. Back out with the trans and the correct throw-out bearing installed. Worked like a charm after that.
For street, and not any killer leg pressure needed, you want to use a diaphram style pressure plate. You can use a 3-finger Long or Borg&Beck style, but these are rough on your leg as they require a lot of pressure. They have higher clamping forces, but really not needed for a street build unless you have a lot of HP. Used a Borg&Beck in one car I had, it worked great and never slipped, but even in my youth, it would wear out the left leg in stop & go traffic.
Discs have 2 different spline counts, 10 and 26. Most have 10 splines on the input shaft while a transmission like the M22 Rockcrusher uses a 26 spline input shaft. So look at yours to verify.
You want a "sprung hub" and a "marcel" between the two disc halves to absorb the shock forces - which most street clutches have.
They offer dual disc set-ups, but have never used one and don't plan on it. A single disc will get the job done.
Brand and type of disc material is open to opinion. The manufacturer will typically state the HP rating of the set-up. I see mixed choice of clutch facing materials such as organic, ceramic/organic, kevlar, etc.. Read here: Clutch Friction Materials Explained - Organic, Kevlar, Ceramic, etc.
Organic is probably best for street. I had a Kevlar disc in my last build because it was recommended by my machinist. It was OK, but did chatter when letting out the clutch to take off in 1st/ Otherwise no complaints.
Year One, Ames, McCleod, and others all offer what you need. Talk/email one of these guys and you will find what you need. I would not use NAPA or other local parts suppliers to get my pressure plate and disc as they are most likely inferior UNLESS you are purchasing a brand name set-up through them.