Motorcycle Repair: speedometer and tachometer ratio, 1976 honda cb550, proper ratio

Question
What are the ratios of the speedometer and tachometer of my 1976 Honda cb550 K  sohc?  My son is rebuilding a used one and trying to turn it into a cafe racer.  He found some small speedo and tach gauges that come in various ratios such as 2240:60, 1:2, 1:7, etc.  Please help us identify the proper ratio so he buys the right one online and doesn't have to try returning later!?!  thx

Answer
David, I've never been asked this question before so I don't know the answer.  There's an easy way to find out. Pull the tack cable off the head and count the number of tack drive revolutions for 10 turns of the crank, Then divide the number of tack revolutions by 10 and you'll have the ratio.  You can do the same for the speedometer.

Sounds like fun.  Happy Racing

Rich