Have 73 mustang 351c what is the first thing I should do to car to get more power?

 

2V or 4V?
if its 2 venturi (2 barrel) then find 4V heads, I don't think there is much out there intake manifold wise for cleavlands, but there are a few, but an aluminum one would be nice. Then look for a good 4barrel carb, or use a motocraft 4 barrel from a 4V cleavland.