I know this isn't that same but, I have a comp cams xe275hl in my stocker, 69 340 daily driver that I do randomly take to the track for fun as I'm a performance guy. Mine will not rev either, it's the cam. I've changed springs and shimmed until my hair falls out diff pre load etc etc and done everything you can try twice. 5,700 it's over with. Runs 12s but sucks. If I put my solid st21 in the exact combo it will rev up. . The xe275 is a killer daily slash low rpm deal. You fight the same issue I have as a 340 has zero torque. The cam works really good until it don't right where a 340 is wanting to go. Change cam to a solid and don't look back. Just my 3yr combo experience with the same cam.