PME's cam synchronizers use OEM Ford signal generators. The 2 wire is a Hall Effect unit and the 3 wire is a VR unit. You would use the one that's compatible with your EFI ECU.
The only difference between a 351C and 351W distributor is the gear.
Julian, the old MSD cam synchronizer used a proprietary signal generator that output an "unusual" square wave. It was designed to be used with MSD's CPC ignition system. Some ECU's (eg. Electromotive) worked great with it whereas others did not (eg. Accel). The new MSD/Holley cam synchronizer outputs a normal Hall Effect signal but I don't believe they're available for sale yet.
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