Internal or External Balance?

Your old flywheel number is the neutral balance flywheel. It looks from the pic that some material was removed at the lower left. If you also look at both flywheel pics you supplied the flywheels are in the same basic position if you compare the flywheel bolts. That means that the material removed on your old flywheel would be in the same general area as a 360 flywheel. I wonder if your motor was balanced in a shop with the old flywheel? it almost looks like it was.

Did you have a vibration with the old flywheel? If you didn't why did you change?

What Summit part number did you purchase and what number was on the box?

Chuck