FWIW, the speed sensor Eric is referring to is required by OBD-II engine
management systems and was never part of the pre-OBD era Vanagons (unless
equipped with cruise control).  This is not a part peculiar to Subarus, as
even late model VWs have speed sensors for this same purpose, to be
compliant with federal requirements for OBD-II engine management.  Most in-
line 4 cylinder VW conversions I am aware of seem to use older US engine
management systems from the pre-OBD-II era or a non-US system (Tiico) and
may not need the speed sensor.  Steve's circuit has performed well for
several Subaru convertors and makes it possible for Syncro conversions in
particular to operate correctly with the late model Subaru ECU.  Having
performed a Subaru conversion myself I would not in any way describe this
as a "nightmare of engineering" but rather a fun challenge which Steve has
notably contributed to with several electronic adaptations to solve various
issues arising from joining these 2 types of vehicles.  IMHO the
engineering of the Subaru engine and electronics is easily the equal to
anything put out by VW, this from a lifetime VW enthusiast who has never
owned a non-VW product.

Connor
85 Westy/02 Subaru 2.5L conversion
99 Passat 1.8T wagon
85 VW GTI
76 VW Rabbit (long gone)
67 VW Deluxe bus, last of the splitties (wish I still owned it now!)