The truck didn't originally have power brakes. I sourced one of the small dual S10 boosters from a '93 model at a salvage yard and fabbed up a bracket.
I threaded the pushrod in the booster to 5/16-24:
I turned down the end of the original '72 pushrod and threaded it to 5/16-24:
The two rods were joined with a coupling nut and installed along with a C3 style master cylinder that I had left over from another project: