Its hard to know what to do when you don't know what you have to start with. Thats why valve springs come with a installed height number. So they don't bottom out. I can't believe someone took out the adjustable rockers and replaced them with the stamped set. You could replace them with 1.6 ratio rockers, which will give you 2-4 degrees more duration and some more lift. Or maybe you should leave it alone untill you can pull it and do it right from the ground up. If you have stock 273 heads, the airflow will stall around .450 anyway. Did you ever get the numbers from the cam card? I was frustrated trying to make my 273 into a performance motor as well. Thats why I bought the 340. Bob