There are a few routes you can go. Alternator pulse type or a programable using a probe and flywheel tooth count. OR a mechanical as previously mentioned. I also priced mechanical out once at approx. $200 bucks and that did not include a Tach! Bob, did you accomplish this for much less than that? The Angle Drive Adapter for $130 is what makes this expensive. I have seen Stewart Warner angle drives cheaper but do not know if they would work, I don't need an expensive lesson either...
I went on the cheap, I found a 3 3/8 programmable off a semi tractor, bought a probe from Napa and made my own brackets etc. Under $75 total.