Yamaha Lower Unit Compatibility

[Whitey436]

I am curious regarding a lower unit from a 1991 Yamaha 150TXRP being compatible with a 91 225TXRP. I have the service manual and the illustrations are calling out that from a 150-225 it is the same drawing.

I am comparing the specs, lengths, you name it on the lower unit it shows the same, yet there are different part numbers when you go online.

If the length of the shaft is the same and the spline count is the same on the two lower units.. would they not be compatible?

THanks!

[boats.net]

They are the same except may have different gear ratio.