The following 2 pictures are of the Proportioning Valve bracket and the Distribution block bracket.
Both were original to my car and were not touched until I took them off last year to restore them.
The Distribution block bracket, (on the right side of the picture) which sits attached to the frame almost directly below the brake booster was definitely originally plated in a Yellow Zinc / Gold Iridite plating. It was a little hard to tell from the exposed side, but once I saw the side that was against the frame all these years, it's pretty obvious as you can see.
The Proportioning valve bracket, on the left was in no way a 'Gold Irridite/Gold/Yellow Zinc' plating.. I've seen many restorations where this is plated gold, even the plater who worked on the brakets wanted to plate it gold, but I chose to use what I thought was the original plating, which as you look at it seems to be a black zinc plating. Even the underside that was not exposed shown no sign of gold... unlike the distribution block bracket next to it.
The following are some brake booster marks, tags and associated detail. Not sure what the 'SK' tag relates to on the booster vaccuum line, but it's easy to replicate. Some pictures provided by Ken Millington and Larry Monk
The following are restored brake master cylinders & boosters off of various 1969 H/O's.
Notice on some of the boosters, 'Delco Moraine' is stamped in the upper right corner of the booster and some it's not. Apparently, which my car was one of them, the booster can also be installed 180 deg clock position, so 'Delco Moraine' is in the lower left portion of the booster, and the wording will be upside down.
The following are pictures from my car. The first one shows the 'upside down' 'Delco Moraine' on the booster and the second one shows the black zinc plated proportioning valve bracket. Also notice the replicated 'SK' tag. Printed it from my computer on a section from a manila folder, worked great.