[Diy_efi] Rotary hall effect SYNC sensor

[T S]

List readers:

There is a rotary hall effect SYNC sensor used by MSD on their "CPC" 
systems.  The sensor is used on their "cam sync plugs."  I'd like to find 
out what the OEM application for this item was, but all MSD will say is it 
is proprietary.  This sensor makes for a very compact design and I'd like to 
know the original app is so I can obtain the part and make my own SYNC plug 
for an engine not supported by them.  The MSD web page for the "cam sync 
plugs" is here:

http://www.msdignition.com/ignition_27_d_8522_8506_8521.htm

It appears to be something that was used on the cam carrier of an OHC motor, 
but I dunno.  Honeywell, American Electronic Components, and PowerComponents 
make similar looking and similar functioning parts, but all of them have 
internal stops that will not permit continuous rotation.  Clues anyone?

Thanks for reading,
Tom