This is what my buddy did on his 86 runner:

... A dual-diaphragm brake booster. Most earlier Toyota's like mine came with a single diaphragm booster. Around the early to mid '90's, Toyota started using dual diaphragm boosters, which provide even more vacuum brake assist. I picked up a dual-diaphragm booster from a '97 T100 4x4. It was the same over all diameter as my old one, but 1" thicker and still bolted right in. The bigger booster made the pedal feel a little softer again, and the pedal effort needed to stop the truck decreased quite a bit. The pedal only needs to be depressed a fraction of the effort and distance of what it used to.