im really shocked to read what ive just read from some of you...
ALL 273/318 HEADS HAVE THE SAME PORTS
SOME ARE CLOSED CHAMBER LIKE THE EARLY 273 AND LATE 302, AND THE REST ARE OPEN CHAMBER LIKE THE 68-85 318 HEADS.
IF YOU GO FROM CLOSED CHAMBER 273 HEADS TO 302 HEADS, CONGRATULATIONS... YOU'VE JUST WASTED YOU'RE TIME AND MONEY.
A better head than all of those is the '234 casting 1967 318 truck/motor home heads, they do not have the heat cross over port in the exhaust which can hurt flow on one port in each head....though still the same intake port as the rest.
I have a question since you have done a bunch of research on different small block heads. A couple of years ago I had a 273 HiPo short block and I set a pair of the magnum heads on it to see if the pistons would clear. They cleared(I dont know how much because I didnt clay check them) but at the time I was thinking that with a stock magnums flow numbers and the smaller valves that they have maybe I could bolt a set on a 273 and make some power with them. Have you ever seen anybody try this? Would the stock magnum valves clear the small bores of the 273? (I know when we used to put 340 heads on we would notch the bores) I was always curious if this combe would yield significant power gain oor if they would be too much. I sold my short block so I never got to try this combo although I have spent time wondering.