The tooth count is stamped right on the speedo gear, the plastic one on the end of the shaft (mine's green) The tooth count on mine is 34, yours may vary depending on your factory gearing setup. The aluminum flange that has the O-ring and installs in the hole has number groupings stamped in 3 or 4 locations around the rim, IIRC it's 28-31, 32-35, 36-39, etc. Each location with a number grouping is oriented at 4 opposite "compass points", i.e. 12 o'clock, 3 o'clock, 6 o'clock, 9 o'clock. After reading how many teeth your plastic gear has, install the aluminum flange with the number grouping that includes your gear teeth number at the bottom of the case hole (mine has a small cast bump there, indicating the line-up point). The aluminum flange also has detents around the ring that will match up with the thin steel "fingers" of the wishbone-shaped hold-down tab, the one that attaches with the single bolt. You can only install it in one of 3 or 4 positions and have these fingers slip into the detents.
Once you understand how it's supposed to go in, it should make perfect sense. Hope that helps.
