Install an aftermarket tachometer on my 1980 KZ75

OK-Here's another one I can't find in the back pages of the forum,but here goes.
I am installing aftermarket gauges on my 1980 KZ750E bike,and I have figured out from different sellers on eBay,that for the speedometer(I am keeping mechanical drive),I need a unit that has a 2240:60 ratio.
What about the Tachometer though?No one on eBay seems to know this(again I am going with mechanical setup).I have been told it is one of these three ratios: 1:4,1:5 or 1:7.Matt at the Kawasaki shop checked the cylinder head cover and found out that the tachometer drive gear is 10 tooth,but we can't figure out how many teeth is on that helical gear that is part of the exhaust camshaft.I've had it out enough times to do valve adjustments,but never checked that. :blink: Does anyone know this so I can figure this out,or am I on the wrong track on this. Or if anyone knows what ratio it is,then I can go ahead and get me the right tacho! :woohoo: Thanks in advance for any knowledge on this!

From what I have read it should be a 1:5. According to DCC this tach would work.

www.dimecitycycles.com/vintage-cafe-race...ometer-15-0080w.html