I have an IH C and a John Deere lawn mower that didn't come with an hour meter. I simply wired in a cheap 12v hour meter. I feel an hour meter is needed for oil changes.
You can buy an after market digital tach/hour meter that picks up spark plug pulses. Don't get one that has an internal battery. Mine didn't last very long, battery problem. The battery was soldered in.
These are cheap options you may consider if you can't get a proofmeter to work.