Making power out of the 318

Yes you could but how available are 273 heads and how much valve can you put in them?
Port flow volume is just part of the picture. Flow velocity is also important and where in the port you get that velocity. Flow volume and flow rate combine to generate port energy. This is the important number.
People keep on saying port volume of a 340/360 head is too much for a 273/318 (velocity) but is that based on any real world evidence or just assumptions? Or peoples poorly tuned engines and or combos blaming the head or cam or etc..

You build a 350 hp 273 vs 318 vs 360 with the same head there all gonna be at different peak rpm I bet the velocity will be similar.