On to some details on some of the differences (not all) of the 1948-52 and 1953-55.1 SM318's.
First is on the "clutch gear" (transmission main drive). The first pic below shows different descriptions and part numbers between the early and later SM318's (prior to 1955.2 Series changes).
Second is on the roller bearings for the clutch gear to main shaft. The 2nd pic below shows the part number and quantities for the different early and late designs. The
Early & Late large diameter rollers (14 count) are the same in both versions, but the
Late design also uses the skinny diameter rollers (24 count) as we previously discussed.
As mentioned, there are other design differences, including the gears and synchro hubs, etc. primarily due to the difference in main shaft thickness. It might be easier to address those individually as needed for pieces you find you will need to replace because of wear or damage. Will be glad to help with that when you get to that stage.
Bottom line is you won't find much to swap between these transmissions to fix up your existing later design one unfortunately.
