I'd suggest finding the best initial with the dist you have so you can then shorten the slots while you have it apart to get 36 total (the dimention is in the archives) but go a bit less then creep up on it then grab a JY RB dist & take it apart & clean & lube it & set the lower shaft end play to .005" with 1/2" ID flat shims or washers from a hardware store or www.speedwaymotors.com has a kit for cheap. Add a shim down on the nub in the center where the clip goes to reduce the cam plate axial play. Toss the heavy spring with the elongated slot on one end & work on spring tension staying just under the pinging point at WOT then plug in vac adv & work with it (2 adjustments). This'll give you a far better setup than anything you can buy & shaft/bushing wear is negligible on electronic units & if the guts ain't all rusted out you have a perfect base to work with for far less money than ANY new item that is currently offered. . There is alot of gain to be had by dialing in the subsystems IN ORDER