There should be a serial number on the drive starting with “27xxxxxxx” and then often a letter like a “B”. The tag is on the upper unit on a tag near where the U-Joint bellows connect. The tag will have the serial number and the ratio as well. Choices are 2.15, 1.89 or 1.61 ratio. If the drive works at all, you can turn the input shaft and count how many revolutions the prop shaft makes. So a 2:15 means that for every 2.15 turns of the engine (or the 270 input shaft) the prop shaft turns once. Smaller 4 cylinder engines like the AQ130 usually had 2.15 ratios, but larger engines often had small ratios (I.e. the prop turns faster).