Just about any 4 cyl petrol rev counter will work, theres normally 3 wires on the electronic ones, one is live with the ignition, another chassis ground and the last goes to the wire on the coil that goes to the dizzy points, thats about it.
Smiths guages have red, black and yellow, the functions of which are the same order as above.
Diesel tacho's run off the alty w connection or phase tap, making a phase tap is easy enough if the alty has not got one, but your better with an ignition driven tacho on that, belt ratio's, number of poles in the alty are a ballache with belt driven ones.