manual brakes???

Are you running a factory mechanical fuel pump? If not, You might put a cheap mechanical pump on there and install a vacuum reservoir. Hook the brakes to the can, hook the intake of the pump to the can and hook the outlet of the pump to manifold vacuum.

(They actually used to sell "dual diaphram" pumps back in the days of vacuum wipers. basicially it was two fuel pumps, one pumped fuel, the other pumped "vacuum")