65 barracuda no bottom end need opinions

Hey welcome. As Rob said, sounds like mismatched parts. The heads you are using have are big port 360 head. They have very poor port velocity on a street driven 273, plus the cam is to large. And if the pistons are .050 down in the hole you have a low compression motor. I had a 67 273 just like your's and it ran quite well. I had my heads angled milled to a closed chamber with the small 1.78 valves, and a 208 duration Hughes cam. I still have the heads if your interested. Bob