been awhile since i had the tach out of my to-35 but i did not take the dash off, now that would be a big job, you would not want to go there.
take breather canister off, just a couple of bolts and breather rubber boot
you have only two nuts to remove to loosen the tach bracket and its off.
good time to pour graphite down cable and lube tach cable.
I just turned tach upside down and poured dry graphite into tach cable hole.
tach still works, hour meter quit at 4K hours about 20+ years ago.
just a little time and some money is all that seperates you from an operational tach.
be sure to keep that gear drive lubed on the back of the generator.
(vendors think a lot of those old gear drive generators.)
note to file: while you have the breather canister off, turn it upside down and soak it in kerosene for a day, (5gal bucket) you will be surprised how much dirt is lodged in the old breather canister.
after cleaning let it fully drain, then oil it good and the little tractor is thank you for it.