I'm using a factory booster out of a 05-06 tahoe that I pulled out of the junkyard with all the hoses for $40, 80's vette master cylinder (new), and love it. Still have 70s style front rotors and stock rear drums.
My car is completely hacked, so unsure of how it will bolt up to your factory setup (ps pump & box fittings), the post Brian linked above will probably answer those questions. The hydroboost I have fits well, I used the firewall bracket from the tahoe, removed the pressed in studs it had (and filled in those holes), then drilled 4 new holes to work with the chevelle firewall.
Showing original bracket when I was pushing out the factory mounting studs, also have a bracket I was initially going to use, but didn't.
welded in holes, drilled 4 new holes to work with chevelle firewall mount, test fitting (also made custom mount for clutch hydraulic cylinder)
Put stick on insulation between bracket and firewall to seal it up (large nut on booster is just temporarily holding it in place)
Installed, you can see how nicely everything lines up. I had to use a drift punch and hammer to tighten up the large nut on the booster. Have about 12k miles on it now with 0 problems.
If you're cheap like me and re-use the factory lines it looks like medusa's butt, but it works perfectly. You can clean it up with custom hoses, I just haven't got to that point.