the only high performance part in the whole rebuild was the ignition modules we used - they provided 20 degrees of advance, all in by 3200 rpm....we actually lowered the compression a bit due to the pistons that were available....
the huge reduction in back pressure really let the engine breath much better.
Overall the fuel consumption improved a bunch.....but we didn't have the luxury of time to make detailed measurements after each mod.....we just used the floscan and a vacuum gauge.
Going from memory, the biggest economy improvements were made in the carb tuning......getting the correct power piston springs was probably the best. there may be a few more gal/hr to be saved with further tuning though we haven't obtained all the parts yet...