Hi,
lyle11, You need several parts at the Battery Ignition unit for the tachometer drive.
Below is a page from the Cub parts manual showing the tach.
You need parts 9 - 13 for the drive. Plate number 9 has a hole in it, and it needs longer screws than the cover with no tach has. The screw size is at the description for 9.
http://www.farmallcub.info/manuals/cub_ ... 011-02.jpg
You may need to remove the Battery Ignition unit to put in the screw toward the engine, the drive sticks out of the hole, and you may not be able to get to it to tighten it without removing the Battery Ignition unit. It's better to turn the engine to number 1 cylinder TDC before removing the Battery Ignition unit, so you don't lose the timing position.
Don't tip the front of the Battery Ignition unit down when off the engine, the drive shaft will probably slide out onto the floor.
Put grease on the tach drive parts when installing them. Grease the drive cable so it turns easily.
The bends in the cable should be gradual, so the cable can turn easily.
The drive cable goes from the tach, along just above the bottom edge of the left side of the hood, and then over the top of the Touch Control unit, to the right side, and around the oil filter housing, just above the oil gauge, to the Battery Ignition unit.
The right length cable fits about exactly in that position.
Below is a link to a post from August telling about the Cub tach.
viewtopic.php?f=1&t=115561