well if the tach out of a v6 wont work with a 4 cyl then i doubt wither will work with a V8 without modification... even then idk how u would mod it
The stock tach can be used, it just needs to be recalibrated by adding the correct ohm resistor or an adjustable one into the tach wiring.
Heres an easier solution,,, Tachometer Tach Signal Interface SGI-8 Dakota Digital - eBay (item 390269556797 end time Mar-06-11 08:16:59 PST)