I have the 1975 280 sedan. It has a diapragm vacuum pump driven off the RH cam on the front of the engine. It is a boost for the brakes and the rest of the system. Funny, though, after replacement, I drove it hard and still puffs smoke on slowing. Could be some residual oil still in there somewhere. We'll see. I was hoping it wasn't valve guides.
No shame in not knowing every model, Larry. Too many versions-too many models. And, I thought I had a handle on the various quirks of automobile behavior. But, my connection in Salt Lake City keeps me amazed at the variations of problems and solutions. Best Wishes, Steve