I just got done scanning this picture of the two different number 25 parts lists and noticed you already posted a picture of yours talking about the different name ( The Massy~Harris Co.) and ( J.I.Case Plow Works, Inc.) Tom, are you catching this? now there is another version to add to your list. This picture is just a bit clearer so you can see the differences in the tractors.
I don't know if you noticed it or not but I looked at these books about 100 times before and just now noticed they are two different tractor pictures. The Plow works tractor has the earlier wheels and the Massey Harris has a taller air stack and no crank on the front.
I still can't figure out the earlier post about the cam shaft change on tractors 57208 and up. I looked in later book Parts list number 26 and it says this new part number 5667A is a camshaft with Gear and if you want just a cam shaft only to order part number 4770A. In the earlier Parts list number 25 ( these two books pictured below ) it lists the cam shaft as being part number 5214A so for some reason there was a cam shaft change in there for reason. I haven't had a later 20-30 apart, is the cam shaft gear put on with a key way and bolted on??