If it's a case of failed instrumentation, perhaps this recent thread will be of interest for you.
To go full on mechanical tach you'd have come up with a gauge which is REAL tough to do if you wanna keep the monopod, but not so much if you want retro dual pods (1970's era gauge head IIRC but then you gotta figure out what to do for all the other instruments 'cause they'd go out the door with the monopod), and a drive cable + the water pump that has the tach drive stuff in it and whatever is in the timing chest to spin that drive in the water pump.
Really not something you're gonna want to do on a whim IMO.
I'm with Tifosi: that just doesn't make any sense. You'd need to figure out how to run a cable to the tach, which with the monopod won't be at all easy. An electronic tach is going to work better and be simpler to install.
Either fix your existing one or have it redone with new guts is my advice. You don't say where in Northern California you're at, but if you're anywhere near the Bay Area call Kris at Kris's Mobile Speedometer: he's great and I'm sure he can fix what you've got.
There is a thread on the BB about dismantling and adjusting an electric tach that reads low. Mine has this condition, but it doesn't bother me enough to dig into it. The poster also notes possible failure points that could be the cause of an inop tach, and which can be repaired.
I was looking at replacing the electronic tach with a mechanical not because the tach is bad,I was looking at changing the gauges for a custom look.I have a spare mechanical tach that I was looking at installing instead of the electronic.Thanks again for the input !
The mechanical tach on 78 and earlier Alfas is driven off the end of the idler pulley in the front cover. There is a gear that drives the mechanisn that bolts into the water pump. You would have to disassemble the engine to change that idler gear to one from a 72 to 78 2000 engine. That is the only part that will work.
I have a fairly new tach cable in my 74 spider. It seems a bit loose (can be wiggled). I am finding oil around the area and I am wondering if there should be a piece in the end of the cable to keep it firm and keep oil from getting out. Any help is greatly appreciated.