Show me your tach placement and ideas !
No pics - description only.
Years ago I mounted the aftermarket tach in my old '69 340 Swinger to the driver's side sunvisor mount. The wires ran down inside the A-pillar cover.
I got stopped once and cited with a "fix-it" ticket with the cop claiming the tach obstructed my vision (it didn't). So I wired in a quick-disconnect plug, got the ticket signed off, pulled out of the police station parking lot, took the tach out of my glove compartment, plugged it back in and drove away. Never got bothered again.