Camshaft suggestions

With adequate porting and 1.88 or 1.94 valves in the 318 heads, they’ll rpm quite a bit better. Are yours leaded fuel 675 castings? If so, going to need hardened exhaust seats, which if so, is more $$$ that would be better spent on a good head. Depends on year rear axle ratio. Tell us about the rest of your car, four speed/automatic, if automatic, what converter, rear axle ratio. The math on mile per hour is tire diameter X RPM / 336 X axle ratio.