The big sixes had serious balance issues, so be very careful about hotrodding them. I worked at a machine shop some time ago where we sort of specialized in keeping some older GMC's running for companies that wanted to nurse a few more miles out of these oldtimers. We found that unless some pretty strict weight-matching was done on rotating assemblies, they would break crankshafts and have other catastrophic failures. The higher compression might make a little more torque, but it would demand increased-octane fuel, and lots of it! A carburetor upgrade and/or porting or valve work would allow more RPM, which would result in the engine launching parts in all directions in a hurry. Exceeding the rated RPM on the big six was a death sentence to every one I ever worked with. These things are low-RPM torque monsters with a huge appetite for fuel, and hotrod tricks just don't work on them!
Jerry
