Snowmobile Tach for my 1975 Johnson 70 hp

[MokiCruiser]

I recently bought an old boat and motor (1975 Johnson 70 hp) and am in the process of restoring it to usable and presentable condition, not a show piece mind you but something I don't have to launch in the dark for fear somebody might see me in it. OK, apart from the humor, here is my question that I hope somebody has an answer for. It has no gauges, and I thought a tachometer would be useful. Looking at some made for Johnson's that are for sale, they are quite pricey, even at Ebay. So as I started looking for alternatives I see that there are quite a few bargain priced snowmobile tachometers on Ebay that can be had with shipping for $15 to $25. Many say they are 6 pulse and I believe (from searching I-Boats) that I need a 6 pulse for the 75 Johnson. So is a snowmobile 6 pulse the same as a Johnson 6 pulse or is there a difference? I have one in my Ebay watch list right now and I'll add pictures from it. Looks like there are just three wires in the harness and so assume that red is the 12 volts, black would be the ground, and the yellow one would be the signal (the brown wire in the 75 Johnson). So would this snowmobile tachometer work and am I correct in where the wires would go on this tach?