I would. What does the gear look like? Is it worn? You can replace the gear and the module (SP?) on the side or just replace it. I would get a MSD. With a rebuilt engine why chance a weak or inconsistant timing spark. A worn distributor will cause the spark to wander..IE when setting the timing does the "mark" move around (bounce around) a few degrees? If so then that is a worn gear and needs to be replaced. Setting timing at 12* means it will fire at 10*-14* .