Ok I picked up a complete bravo 1 drive. Trying to figure out the gear ratio by the SN
transom number is OD 3355167
the SN on the upper is OD 329093
thx

Mark the drive shaft and prop shaft, put in gear (F/R doesn't matter)

Rotate drive shaft 10 times and count prop shaft turns then divide by 10

0D329093 = 1990 Stern Drive R BI-ROTATION BRAVO 1 [1.50:1] Model number 5120150CS

BRAVO DRIVES - 0B664190 THRU 0F729999 (mercruiserparts.com)

Thank you.

^^^^^ As long as someone has not changed the ratio