Will 318, 340 or 360 heads fit on a 273?

273 & 318 have the same size valves. the 273 heads will NOT have hardened seats for todays unleaded fuels. I'd put 318 heads on it with hardened seats. A good pair of 302's would be nice IF you can find them not cracked. Otherwise, I think I'd just go with a typical 318 smog head. You can bolt any intake you want on them.