1973 dart sport brake booster
For your consideration:
Lotta motors I put in don't have enuff vacuum for a booster.
I have always tossed the booster and put on a small bore manual master cyl, Raybestos 36406 when avail.
It's straight bolt on, you'll need a pushrod from Mancini?, (make sure it doesn't bind at the pedal pivot bolt.)
The small bore gives more "mechanical advantage",
I have also been known to use an "alternative master cylinder, and I don't see why not an alternative booster" out of the auto wreckers, sometimes requiring fabrication", especially with your location.
Good luck
https://www.rockauto.com/en/parts/raybestos,MC36406,master+cylinder,1836