Different suppliers ... different part numbers.
It may fit your 125Hp Force, what you have to check is if your engine has 1 piece drive shaft gear case or 2 piece.
In those years 1988-89 Force had different gear case at the 3 and 4 cylinder engines.
They changed from 1 piece drive shaft to 2 piece in that time and maybe a pre owner have change the LU.
I have a 1988 85Hp Force that should have 1 piece drive shaft LU from factory BUT it has a 2 piece.
There is different impellers for these two.
Mercury suppliers has OEM impellers and maybe kits, this site (Sierra brand) or Mastertech marine has aftermarket impellers and kits.
Important is 1 or 2 piece drive shaft LU.