Downunder, I have an extra tach if you confirm that yours is toasted. Before I'd buy and ship another one, though, I'd check to see if you can get yours repaired locally.
I installed a MSD ignition and wired it wrong to the tach. Local "experts" told me the MSD Tach Adapter was pretty tough and probably not the problem. This turned out to be total Bull$#!+ as these posts confirm. I purchased another tach and then a new Tach Adapter which solved the problem. I know this tach is OK because it was in the car when I got it working. I then switched back to the original tach which worked fine as well.
I don't know if there are different tachs. Mine matches and works correctly in a '72. Yours may be different. The indicator lights may not be the same in a later car.
Anyway, it may be an option.
Mooso.
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