1973 340 Cam advice

I'm not really a fan of any gear below 3.55 AND your current tire size as I would consider that the absolute minimum. And only because you have the 4spd manual behind it.

IF that is going to be the running gear, I myself would wait until you see how it is with the stock cam inside the engine.

As a point of flexable intake and carb to use for now and later that would cover all the bases, I would ether keep the OE intake and carb IF you have it for the 340 or make a move to a RPM & a 750 Holley DP as a base min.