siliconix printed an ap note on usinf one of their dvm chip pairs as a
digital dwell tach.  this was in 1988 os so.  i used it in the design
phase for my advanced design project in college.  i added an lcd to the
circuit using discrete chips (exclusive or and 555 timer for the phase
and backplane drive circuitry).  you had no "all in one" chips back
then.  lcds were just becoming on the scene.

the circuit used a one-shot and some other simple circuitry to convert
the dwell.  you would have to couple the higher voltage of the new
ignitions to the circuit.

it you are still interested, i will lokk thru the files for the app
note.


roger