Are there different lower units for an Alpha Gen 1 drive?

[rcspencer1]

I need to replace the lower unit on my Alpha Gen 1 drive, and just wondering if they are all the same or if I need to specify something to make sure I get the right one? Maybe a silly question, but I'd like to be sure before buying... Thanks

 

[achris]

Yes, there were 3 different lower gear housings. 2 are the more common and their ratios are very close, but the 3rd is significant. What engine do you have and what is the current drives' serial number?

 

[thumpar]

The ratio is the only difference.