Plus with a 318, you can throw on a set of 340/360 heads with the bigger valves and let it breathe better...
You can't put larger valves in the 273 with the smaller bore unless you notch the bores for the valves... But why do that when you could run a 318 instead, and they are plentiful...
I've run 318's with 2.02" intake valves and 360 heads with 10.5 pistons to get the final compression to 9.2 which is perfect for a street engine...