Brake Booster Replacement

I finally got my 1975 CJ5 running decent and it putted around town under its own power for the first time in probably 4 years yesterday.

That being said, the brakes need some work. I think my issue is a bad brake booster. The brakes seem to work well and be adjusted and it has all new brake lines. At some point it got a dual master cylinder and vacuum booster.

Now with my foot on the brake pedal, the Jeep idles up and I can hear what I presume to be a vacuum leak. So my question is, how do I know what booster to get to replace it? Since I don't know where the booster came from am I going to be better off just getting a whole new set up with the master cylinder included?