Best brake booster

Drums are said to be self-energizing. That is to say, as the car slows down, you gotta relax the pressure on the pedal, else the car will slow down faster than you had anticipated.
Discs are not like that.
It always requires more pedal pressure to slow down faster. Because of this perceived "lack" of self-energization, disc-brake cars almost always come with boosters.

LATE A-bodies with 10" drums stop pretty well on the street, with a good feel, and in my experience, an easy pedal. But, that 65 of yours is pretty lightweight, and it doesn't really need more brakes than 9inchers with decent organic shoes. A booster will however, reduce the pedal effort.

If your pedal takes a lot of travel before braking starts, or,
if the pedal is not hard almost right away;
I would figure out and fix the whys of that first.

For instance,
if the parking brake cable does completely relax and the strut remains partially extended, the rear brakes will become "spongy".This sponginess will telegraph into the brake pedal, and it will require more pedal-travel and more leg-effort to stop the car on what then is, pretty-much, just the front brakes.
With an all-drum system, AND a single-piston M/C, it is essential that
> the brakes are all working properly; both hydraulically and mechanically,
> and that all are properly adjusted; including the parking system, and
> that the pushrod entering the M/C is the correct length, and especially, is not too short.
> and that the pedal is high and hard.
after that,
> if the brake shoes have been cooked, throw them away. Or if their curvature does Not match the the curvature of the drums, make it so. This requires you to take the shoes and drums, all of them, to a brake specialist, who will grind a proper curvature onto the shoes.
>The shoes have to be able to grab the drums in order to slow the car. If the friction material is glazed as in polished smooth and/or cooked, or if the shoe contacts the drum in only a small area, then stopping will be made more difficult, requiring
excessive pedal pressure.