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According to the way I am reading the 1970 Johnson Common Parts Reference Guide the only difference between #375861 gear set for RD-10 thru 19, RDE-16 thru 19M & RJE-18 was the pinion gear #375835 with tapered bearing, shim and cup.
The RD-19, RDE-19, & 19M & RJE-19 took gear set #376996 with the only thing different being the pinion gear #308692. Forward gear #375759 & reverse gear #302517 stayed the same in both gear sets. The #308693 pinion gear dropped the tapered roller bearing and went to the larger gear stub with full radial bearings. That newer pinion gear is used into the 1970s 40hp according to the guide.
Just another tip: the forward gear & reverse can be swapped in position if the forward gear bushing is pressed out (a little heat helps) and pressed back into the reverse gear. The reverse gear bushing is easily removable. Once this is done the gears can continue to be used in spite of shifter wear at the lugs. Similar to turning the shifter around.
I just finished building a 1955 Big Twin with these fixes. The only odd thing I ran into was a small driveshaft bearing under the water pump. It was pressed into the housing. Luckily I had a bearing of same part number to replace it with. I think it was a Torrington 1012-BH. I have not found this bearing illustrated in my parts break downs, but don’t have every book?
Any comments appreciated?
Dan in TN