273 2 barrel pistons are about 9:1, 8.8:1, compression ratio. 273's were all done by 69. 68 and 69 273's had .020 higher pistons to keep compression up with open chambered 318 heads. They were never SMOG engines.
66fs, I just saw you are from Greenwood SC! My folks, both sides were from Ninety Six, what a small world. I spent many summers down there and I had such great memories visiting all my aunts and uncles and cousins. Then my next door neighbors daughter decided to go to Lander when I lived in Yorktown VA. She told us and said, it's a small school in a small town, you might not know anything about it. We said, oh yeah we have.