Ok! Before you start you need to understand the design.
That lower unit uses two tapered roller bearings to support the drive shaft.
On ALL sets of meshing gears there must be a specific backlash or freedom of movement before the teeth engage. This is because there is a specific spot on the gear teeth where they must mesh. Too much or too little backlash and the gear teeth will wear even in the presence of sufficient oil.
Back to your lower unit: The top bearing is spaced by shims and sets the gear lash. Since this is a VERY old design the top bearing is held in place by a circlip on the shaft. The bottom bearing slides on the shaft. To ensure correct pre-loading of the bearings the pinion nut must be torqued to the correct specification AND must be a self locking nut. Since self locking nuts do deform with use the locking factor is compromised when you remove the nut. THUS: A new nut must be used when you re-assemble.
Now, It has been years since I disassembled an old lower like yours so bear with me. I know for certain that the bottom bearing slips off the shaft. The top bearing MAY be a slip fit or MAY be l light interference fit simply located by the circlip. At any rate if you want to remove the top bearing take a long piece of pipe that will fit over the drive shaft and tap the bearing down. Reach into the lower unit casting and using a long drift and hammer, alternately tapping each side of the race (Called the cup) work it out of the casting.
Just because a bearing is colored does not necessarily mean it is bad. Inspect the bearing and race for Bluing which would indicate overheating, pitting, and wear. If none of these conditions are present and the bearing rolls silky smooth then it is good to use.
If you decide you want to replace the bearing it is a standard one. The numbers will be stamped into both the internal and external race. Take the bearing and race to your local bearing supplier.
To re-install the bearing if it is a light interference fit, heat the inner cone over a 100 watt incandescent light bulb for about 15 minutes. If possible cool the shaft in a freezer. Then, with the circlip in place and using a thick glove, quickly slip home the bearing.
The light bulb heats and expands the inner bearing without supplying too much heat to damage it. Neat little trick.
