You are about to enter the real world.

If I was doing it, had the time and equiptment, and enjoyed it, I
would first
use a scope on the pickup at various speeds and see what the
pulse
really looked like. (don't know if it would be wise to hook one
up to
a running engine though).  Then maybe load the pulse down with
different
values of resisters to see what effect a load would have on the
pulse.

Having this information, I would build a digital to analog
circuit and control it
with a PC.  Using this test circuit, test the various circuits
for zero crossing
detection.  And maybe even distort the output from the d to a
some just
to see how the detector would handle it.

Then after the pic is programmed, use the same setup to test the
pic's
program.  Then after all this and if (and only if) the value of
the antique truck
hasn't increassed to the point that you would loose money by
installing
a non stock item in the truck, I would instal it.

But then I allways have had big dreams that I never carried out.
Does
anyone need 27 tons of river rock?

Bill C.   bill@cornutt.com