there is a difference in external balance factor between the LA and mag 360, not sure of the exact amount. cranks are the same, but the mag has lighter rods, pistons, and ring pack which accounts for the difference. but if you put it in neutral with the car stopped, and rev the engine to the RPM points you feel the vibration at on the road, and it DOESN'T vibrate, then you can rule out anything ahead of the tranny, including the balance of the flywheel. it's a cheap test to prevent spending a lot of time and $$ on something that's not the problem.