Use a Chrysler 6-cylinder reluctor and pickup coil for a slant 6 engine to trigger a GM 4-pin ignition module. I'm in the process of building a Triumph Spitfire 6 cylinder distributor that way, and the reluctor and trigger coil are a good fit in the Delco distributor for the Turnip engine that's almost a clone of the Chevy, just CCW rotation. a guy on Ebay sells the whole reluctor/trigger coil unit, new old stock, dirt cheap.
Jerry