Tachometer help needed

Just put a Crane Cams optical trigger kit (trigger,electronic controller and high performance coil) into my '74 dino 246. It runs like a clock, but the tachometer is way off (showing too high). We contacted Crane's and they suggested trying a few different resistors, so off we went to Radio Shack and bought a bunch of different ones. finally found one that seemed to work (tach in car matched mechanic's tach thru rev range), but as soon as I got home it was way off again.

Anyone else do this conversion, and if so, did you have tach problems and/or solutions?