They come from the dealerships parts Dept long long ago. It seems like “ in a galaxy far, far away, as well. I had a buddy that worked at the local dealership that really liked me. He was the owners son and loved muscle cars. I had a 70 AAR and a Superbird at the time. I could go in and buy parts at a slight discount all the time. When Chrysler was going through the turmoil of the 80’s bankruptcy, he sold me all kinds of parts real cheap. They were cheap even for that day. I bought 4 each of the masters cly for my 70 Bird and my 70 Cuda. I also bought four 70 style sure grip units and four 71 brake boosters. The 70 booster was no longer available. One was in a kit like the one pictured. The cost for all this stuff? $25 for each. I bought heads, W2 stuff, you name it. This was before I was married. Hemi stuff was scares and I did not need any of that. Some guys had foresight and money. They bought lots of stuff.