1973 dart sport brake booster

Hey there again. I have run some tests and have pulled the brake booster for the 5th time now. Something is for sure wrong inside the actual booster. I found a rebuild kit online that i think will work. This is around $300 though. I have read other forums and some people say you cant put a dual diaphragm booster on a single diaphragm car, and other sites say you can. At this point i want a booster that will be safe, and something I wont have to take off for awhile. Are there universal boosters that could work? Any info appreciated.