Just go to napa, or any auto part store you feel comfortable with if you want to save some bucks. Here's what I wrote a few months ago for similar question.....
"guys,
I did the conversion, and i don't know who "g-body" is (I do now), but I simply bought a 'NEW" Master cyl. Assembly (with new check valve in the 'NEW' booster) from NAPA for a '87 V8 Regal ($78) and had to only "tweak/stretch" the brake lines just a bit to slide rite in to the new MS. "T" the vac line to the PVC, change the pedal to one from a V8 Regal/Monte, bleed the cyl. on the bench, and revel in late '80s gm brakes. I didn't even have to bleed the corners, tho I did anyway to flush the system.... brakes feel like a cop car impala now.... better than ever..."
To further clarify, you'll need a brake pedal from the junkyard from a PB equipped G-body, Master Cyl as above, plastic T to plumb the vacuum source, and a few feet of vac. line. That's it. I took the 'new' route vs. reman'd as the price diff. was negligible, and I wanted a NEW check valve (which I verified would hold 25+ psi). There is an extra bracket between the PM and firewall that will not be re-used with the vac. setup. All other hardware is used. Changing the pedal ass'y is a bit challenging... it's tight down/(up?) there. Expect to use various open-end/box/socket/extensions/u-joint tools as req'd to get the bolts loose, and remember what arrangement u used for putting them back in. Also, be careful and make sure to use/reuse, and not damage the nylon inserts on the pedal pivet. Seems like I had to somehow lightly tape them in with masking tape while I was replacing the pedal as they kept falling out. GNTTYPE.org has a procedure for the swap. I used it, and advice from Nick Micale (Arizona GN) on the vac. source. I couldn't be happier. Good luck!
