307's were considered grocery-getter engines when they first came out. You can make some good torque for a small engine but those 76cc chambers are a problem. If I remember correctly, the 307's came originally with 64cc combustion chambers which would make the compression ratio over 9:1. That would help give it some guts because with low compression and a cam with overlap, that engine is probably not making good power over 3000 rpm. My advice would be to run it and save your money for the future build of a 350 or 383.