I tore into one of my old Speedmaster II drives that I locked up a few years back to find out why it locked up. You can see where the upper vertical shaft taper bearing overheated and locked up. The gears look fine and dont have any pitting. The bearing that locked up was a Timken HM89410. You can find the bearing for $9.00 but if you look up the Mercruiser part number that same exact bearing is $180.00. That is a markup of 2250% . I can barely see the part number on the torrington needle bearings and there is no part number (that I can see yet) on the propshaft seals. How can I find out what the torrington needle bearing part numbers and the shaft seal numbers are? Would Mercury know what the supplier part numbers are on something that old?

Need to measure the diameter of the shaft with a micrometer and the OD of the bearing. Same with the seals.
A bearing/seal supply house should be able to fix you up from there.

Long story short, pulled a upper gearbox bearing on a MC, Merc wanted $35, Sierra wanted $21, Purvis bearing had it for $9. Take all the bearing and seals to the local bearing house and you'll cut your rebuild by 2/3.

I'm thinking more of a savings than that. Im rebuilding a SSM II drive just for fun.