I think I can answer your question but waited to see of anyone more technically oriented would answer first. I don't think you'll have any trouble finding a working tach for the 544. Just about any electrically operated tach will work with your distributor. About the only one wired differently than usual that I know of is the one in the 1800 series before the E and ES. Tachs that I'm aware of would have 3 wires (maybe a 4th for lamp) that would consist of one plus (+), one ground (-), and one from the negative side of the coil which is the exposed coil connection on your 544 and 122 models. Some early aftermarket tachs may a bit more involved. One of my first cars (in 1965) was a 1959 Mercedes 190 sedan. I was given a Sun tach (the kind you'd put on the steering column) that had a largish sending unit box to mount. It was meant for a V8 and a neighbor with the knowledge soldered in a resistor or two in the appropriate spots to make it read correctly for my 4 cyl. I believe the top-of-the-dash tachs used for the 123GT would have 4 wires as I described earlier. I may even have the makings of one if you're interested. - Dave