TOPIC: Vintage Airguide Tach questions for Mercurys

I have an Airguide Tach (#690) that says it works for 2, 3, and 4 cylinder motors (connect jumpers on back accordingly for 3 and 4 cylinders and leave off for 2 cylinder). Will this work on a 1978 Merc 20hp? if so, does it require something else to go with it? How could I connect one to a non electric start motor if possible?
ALSO: I bought a 1965 Merc 1000. One owner rig that never had a tach and they never changed the prop (3 blade bronze 48-41358-A3-17 on a 15T Powercat). What Airguide Tach works for this IL6? I just have never run motors without tachs except a small fishing motor. Is there some sort of additional sending unit type piece that would also be required (I do have controls for this and a wiring diagram that would help me if I knew the rest). I need help or I will wreck something (and therefore will not do anything if I cannot understand it). I just do not want to over-rev that old 100hp Merc 1000...it survived 50 years and I do not want to fry it with my ignorance since the book says 5,200 RPM max. Anyone out there with a 1965 Merc 1000 with an Airguide Tach I could get a number off of? Any help is appreciated (please forgive my ignorance...previous purchased boats all had them already installed)
Thanks - Dr.Go! (Mark)

I forgot to mention I have not yet run this Powercat with the 1965 Merc 1000. I am hoping to get things right (and get a tach wired) before the excitement of driving it turns to a "smoked motor" because I want to see how fast it will go without a tach.

The airguide 666-B or 667-B is the one you need.There was a NOS in the box on e bay for $ 250.00 that did not sell. It was a couple of weeks ago.

Taco.

Thank you for that information. I was looking at a chart and was wondering if one of the numbers you listed was what I wanted. I appreciate the help...now time to go hunt one down.
Dr.Go! (Mark)