If you search "OER tach" there are six pages of threads, many discussing how/whether an original or repro tach will work with MSD, which I see you have from another thread.
If you have an original 67 tach already and it is in good shape cosmetically, you could always send it to AutoInstruments to have them check it out. If they put it on the signal generator and it works, then you know you have an issue with signal from the MSD. They charge around $275 to build a new tach inside the original, and it will work with modern ignitions. I have HEI and sent my original, dead 69 tach to them, and it works great now.