identifying heads for 273

I had a 66 Dart 273 4bbl with the domed pistons. I retarded the timing and got it to run without pinging on 91 octane gas. The swirl port (302) heads will give you a larger combustion chamber. The 75 and later 318 heads will have an even larger one.

IMHO the best course of action, particularly if you are planning to rebuild the engine, is to install the flat top (2 bbl) pistons. If no rebuild is planned, try the thickest head gasket you can find. (Don't know if you can double up head gaskets on the LA). The advantage of these options is that there is no need to alter bolt hole relationships.

The flat tops are a lot easier to find than the domed pistons. I would be very hesitant to do anything to the HP pistons beyond new pins and rings.