power brake booster

The booster in post 3 is a "dual diaphragm" type. One I took from a 74 Dart slant was a larger OD single diaphragm Midland-Ross type. It will boltup fine your brackets, but may not clear the valve cover, especially w/ a 440.

You can test your booster by supplying it vacuum from another car that is idling. I have done that to test one in the air and verify it follows motion of the input rod and don't hear leaking from a ruptured diaphragm or stuck pedal valve.

Finding them on rockauto can be hit or miss. I jumped on one for my 65 Newport that showed up for ~$80 clearance w/ MC. They had shown none for years. Came in a dusty box, bolted up and worked fine. Before that, I had drilled holes to mount the 74 one. Booster Dewey can often supply one, but not cheap. I have never seen rebuild kits, though that would be easy for a M-R type. I did so by cutting neoprene rubber sheet and it worked - in air, haven't run on a car.

You can also use a newer booster. I installed one for a 95-99 Breeze w/ ABS MC on Dart brackets. Intrepid boosters look the same (not the MC). I did have to rat-tail file the bracket holes slightly.