Here's practically a bolt-on for our trucks with that mc, if it has a void, about 1-inch deep, drilled into its piston-rear. If no void, then even better, as no need to make the 'plug' described below. AutoZone Booster
Part Number: 54-71108, found on AutoZone.com., & made to fit a '79 Chevy truck.
You'll have to buy 3 parts from Lowe's to adjust the pedal length to fit: a *clevis, a threaded rod, and a coupling nut, about $10-$12. *Clevis should be wide enough to accept brake pedal linkage between its holes. May hafta buy one slightly too snug and widen its ears a tad.
You'll also have to make a *"plug"[about the shape and size of a .38 bullet] to fill the void in the rear of the mc, so the booster rod will begin its push where the plug's rear lies approx. flush with the rearmost surface of the mc-piston. *This plug is made from the threadless shoulder portion of a bolt--or a rod--whose size lets it slide around easily inside & is close to the diameter of the 'void' drilled into rear of mc.-piston. This plug takes about 30 minutes to make. Cost approaches $zero, if you can find a proper sized bolt in your junk bin to cut, grind, & fit.
If you don't have a booster core, just go by a garage-or-two until you find a
discarded, for free booster--most any model, I've found--and AZ will accept it for the core value when neatly closed up in their original box.
Just another method that skins this particular cat.......
Have fun.
Sam