Rebuilding a 65 273..I need some help.

The Isky E4 is rated to 5500 using their dual springs but it might not be much bigger than what you have. The E 3 and the Schneider cams are a bit bigger. Just sayin'
Here's a thread that is going right now about a 273 cam. Lots of good information and recommendations there especially the last page. [WANTED] - Help with Solid Cam?