What was the Cat 22 (2F,1935) original starter motor?

Delco Remy 736D is the correct starter.

I did a quick search and found this 39mt as a cross reference. I dont know anything more but here's the spec sheet. [attachment=77850]Screenshot_20241012-071146_Chrome.jpg[/attachment]

I suspect that there are other period starters that would work, but getting the correct gear may be the biggest issue. I put a modern starter on my 22, but had to put the correct ring gear on the flywheel so that it matched the modern starter gear.
Good luck and keep us posted on your search. Grant.

Here is the 736D Build Sheet.
The hardest part would be finding the 1850844 Drive Housing.
 [attachment=77856]736D Starter Build.jpg[/attachment]
 

Which catalog number / grouping (truck, car/passenger, etc.) is that page from, OM?

Besides the info in the header it's from my Delco Remy Service Parts catalog, about 8" thick in screw post binder. The kind you used to see on the counter of old time parts departments.

The 39MT starter in SAE #3 arrangement could possibly work but you would need to change to a 10 tooth pinion which I believe is available ( straight tooth in this application).
I haven't done it so you would be beta tester.

There was an article a while back on the conversation process, including changing over or adding the ring gear.

https://www.acmoc.org/bb/discussion-d72/15214-chapter-9-caterpillar-twenty-two-electric-start-conversion?start=0