Try Caterpillar Legendary Service Literature, Midland Press, 1-800-228-7821.
They have very good quality manuals like the originals.
It appears that Cat never produced service manuals for any of the early diesels. Not until the models introduced in the early 1940's did service manuals appear.
That's what I kinda found also.
You can search for yourself ( in the track tractor section)
http://www.cat.com/cda/layout?m=90800&x=7