The difference is from the machined pad where the crank throw bolts to to the edge of the top portion of the flywheel where you have the yellow marker. It is deeper on the drive side. A air heat gun is plenty, and will never produce enough heat to damage the crank but will expand the inner. It is not just the interference fit on the crank journal but the seal surface to watch out for at bearing removal and installation. It takes very little expansion to make it an easy job.