Want to get a new power brake booster, 1973 Duster.

Meh, for what that thing costs, I'll just get my original rebuilt. I noticed in the description that it had what I suspected, 3 different master cylinder piston sizes. 15/16", 1-1/32", and 1-1/8". My Autozone Duralast NM1571 master cylinder is a 15/16", I guess that'll be adequate for my needs.

My booster seems to work, it has good power assist, but the internal rubber parts are old, if it isn't causing a big engine vacuum leak now, it may in the future. Under the dash panel, the previous owner installed an additional long spring to help return the brake pedal to its unapplied position, and even then sometimes it doesn't fully do it. The previous owner put a red LED light in the corner under the dash, and it lights when the brake pedal is depressed any amount. It is on a relay of course, this previous owner loved his relays. The car had a half dozen relays under the hood for the add-on cruise control and other things, we have disconnected most of them already.