On a stock body I use the rocker as a reference. bottom of the rocker/pinch weld. Engine/trans will be 3 degrees tailshaft down on normal mounts from the rocker. Do not use the carb flange unless you have confirmed it to be square with the pan rail. Pan rail, bell housing or block front machined surfaces. Use a decent digital protractor.
If the results don't match the theory, change the theory.
