As a side note, lean means VERY lean > 18:1, off the wide band scale actually. We added fuel to the motor and each time we did hp increased 3-4 hp with every turn of the adjustment. But, the adjustment on the carbs maxed out and about the best she would come to was 17:1, still dangerously lean according to this dyno data system.

Which explains quite a bit, like why it runs so hot under load but will sit at idle on a 95F day and be cool. If feel that if the motor had more timing or more compression at that A/F we might have seen a BOOM in short order. Larger main jets will be in order to capture the hp left in this motor.

But, for a full 10/10th effort there is still more work to be done on the exhaust and heads as Jeff mentioned, plus timing curve issues with full timing advance being lower than expected.