I went through similar issues on the rebuild of the 70 horse Force.
After looking at parts, over and over and comparing parts, over and over, I finally figured out that many components in the lower unit and gear housing are the same.
Do some searches, compare parts numbers between the two and see if there is any references to components from the 150 fitting Your 90 horse.
I believe that You will find that they may fit, but, do the research to be sure.