I believe it should bolt up, I don't think there is a problem with the flywheel, or starter drive. I keep spares for my D7's, and believe I have a starter motor on the shelf, not sure about any housings, but the Delco electric starter motor number may be helpful in case you can't source both as a unit from a salvage yard. I'll see if theres a tag on it, should be, or I can wade through the snow and look on one of the tractors. I would believe you should be able to source these parts, they were common, all the military 4T's and 3T's that were government purchase order tractors had electric start on the starting engines. I'd take a photo and post it, but still have not been able to load images from my new phone onto the PC.
Hector mentioned part numbers out of the parts catalogs, and those match what my parts catalog shows for S/N 3T1-3T19999 inclusive.
17A, has a different starting engine than the 3T, which has the earlier version that was used on many old caterpillar tractors, including D8 1H's, 2U's and other older tractors, such as the D6 2H, 5R with the 3 cylinder engine, Forty Diesel if I recall, RD8, and the Seventy Five if I recall, good chance to find parts, but you would have to check the parts catalog to see if the 17A used the same one, I am not sure, don't have a 17A parts catalog.