identifying heads for 273

Ive compared the so called #302 swirl port heads with the early 273 closed chamber heads. The 302 swirl port heads have a smaller combustion chamber. So putting a set of them on wont lower your cr and in fact I'd be inclined to believe you will loose flow. The intake ports on 302's have a huge pushrod bulge in them.

What I would do is establish a baseline on what you have now. Partially assemble the engine and put one piston in it. measure the actual deck height and cc's in the block with the high cr piston. Next - cc a couple of the combustion chamber pockets in the 273 heads. Do a calculation using these figures and a couple of different thickness head gaskets, use .026 (mopar perf gaskets) and .040 thick (fel pro gaskets). See what you actually have. You may find that the actual compression ratio is not so intolerable. I think Chrysler always misprinted the actual compression ratios of their engines, they were always lower than what was printed.

If you are concerned about detonation consider putting a slightly longer duration cam in it, that will bleed off some of the compression and allow it to run without retarding it.

Good hunting.