Particular question on replacing gear train in lower unit 1976 25 hp johnson

[dthx]

getting ready to put the lower unit gear case back together.
I noticed that there is a "key way" cut into the gear train bearing and another one cut into the housing that holds the gear train.
Probably for oil to communicate around the bearing surface....
Question...should I lay the gears in the housing with the key ways matching up or should I rotate the gear train 180 deg. ?
Or...have I lost the key stock that goes in those slots to keep the gear train from rotating?

 

[dthx]

I think I've figured this one out...I took another look at the whole unit and I noticed that there are locating pins that keep the gear train from rotating....
I think I'm good.
Question....any hints on how to clean the carbon that has accumulated on the shaft...looks like a hard carbon shell ...(thicker than a film)...