I've always been under the impression that the square tanks were on the R, and the round ones were on the N. The parts book I have only calls the round tank and lists it for the N. There is no mention of the R oiling tank that I could see.
Thanks to everyone for the replies. I thought I had seen some discrepancies in real photos but now realize they were only in old advertisement drawings (attached). Based on the larger ring gear these should be Model N but they also have the square oiler tanks. Also, the old original casting of the Ertl 1/64 scale toy (also attached) Waterloo Boy has the round tanks (Model N) even though the box is marked as a 1914 vintage machine, which was too early for the N.
These were the reason for my question. Thanks again to all.