i have welded up the slots many times, and have had great success doing so.
the one thing that buggs me however, is removing the internal snap ring/spring under the rotor. i finally made a set of pliers that fit the diameter of the "upward pointing" ears, so no more fiddling with two tiny screwdrivers to get that thing out !
i came across a couple of those FBO plates quite a while ago, but i haven't tried to do anything with them.
i need to build a distributor for my charger, but i haven't decided if i will use a chrome box, 6AL, pertronix, or a gm HEI mounted under the housing.
i also have an offshore distributor i picked up at a swap meet one time for $5.00, and it has a ball bearing shaft in it. i might fab up some factory style guts for it, and experiment with that.