Really the early '70s 318 heads will not increase power and may actually decrease it. They don't flow much different and the chamber will be bigger.

Magnum heads would be the best swap, then the late 2-barrel 318 heads with casting number ending in 302. The 302 heads have hardened exhaust seats and basically the same chamber volume as your 273 heads. You can port either head. believe class racers have said the early closed chamber heads can be made to flow better than the 302s.

273s don't get much respect and some of that is economics. They are more expensive to overhaul than a 318 and people are basically giving 318 blocks away. I have been given three, two being complete engines. I would suggest finding a 1986 - 1988 Fifth Avenue as it has the roller cam block and the 302 heads. That 45 cubic inch or 750cc increase in engine size will do about everything better than a 273. And those late Fifth Avenues usually led sheltered lives.

R.