Carefully calculate the static compression ratio and cc the heads. My 273 had new pistons when I got it, it calculated to 7.8 to 1 compression. Pistons 45 in the hole and 65cc chambers. It had 115 cranking with a mild 216 @ .050 and 110 lsa hyd.cam. I tore it down and milled the heads .032 thou and the block about .040 to get 9 to 1. I am currently running a comp 270 solid. With 224 at .050 and .468 lift before the .022 lash on a 110 lsa. With lash it runs more like it has about 10 degrees less duration. Very slight lope and pulls pretty good for a little motor. And 150 cranking compression.
I've heard the Summit cams work well in the small engines.