1990 force outboard lower unit interchangeability

[chevyguy420]

hi, I've got a 1990 force 120 that has electrical issues and I'm having major trouble finding parts so I've been thinking about just getting a new motor. I was able to find a good price for a 1992 force 120 that needs a lower unit. are these interchangeable and also how do I figure out the shaft length. I have pictures of both serial numbers if that helps. thanks in advance

 

[Nordin]

They should be interchangeable.
1995-96 Mercury started to put their LU at the Force engines but they did not look the same.
If the LU.s look like the same, it will fit.
There were long shaft 20 in (L) and extra long shaft (XL) 25 in.
Measure from anticavitation plate to the transom clamp. 20 in long shaft, 25 in extra long shaft.