big cam in stockish 318

Ive got 73 duster 318 727 3.55 gears with 8 1/4 rear end
its got a 318 bored .30 over with stock heads ported to fit intake manifold
holley 750 vacum secondaries, edelbrock performer intake, headman headers, flowmasters, and a mopar purple shaft cam 292/292 duration with .508 lift for both intake and exhaust
Car sounds gnarly idleing but has weak low end power (barley spins tires) and mild high end power

Does anyone know how to make more lowend power with stock 318 heads and would a smaller cam make a noticable power increase