Yup, I've run a mechanical tach in the wagon since before I started racing it in 1995.
I never did make a real mount for it, as the black tape holding it to the steering column has worked for 25 yrs

I removed the black plastic cover in the center of the dash and ran the cable through that area right to the tach on the column. I'd like to make some kind of alum plate that has a clamp that goes around the column. Little more "professional" then black tape. But, like I said...it's been 25 yrs.

I've seen 90* adapters in some old race cars that give you some leeway in mounting the tach and getting the cable attached.
I have some parts gathered up to put one on the blower car. I'd mount it on the cowl or back of the blower? It doesn't see rain, so moisture is not an issue.
Since the wagon is in the garage currently getting head gaskets, I can get a few pictures if you like and post them some time this week.