Rings are plenty clean now. Try 20W50 regular motor oil. That tractor probably originally called for 30 weight, as did many cars from the 40's and 50's. Those people mostly agree 20W50 is the ideal substiture for 30 weight. Give it some time and the smoke should lessen noticeably.
Photos of tractor side panel, tractor engine and, what I feel is interesting, is a close up of the pcv system. Not a bad idea for 1938. Maybe I can call Sears and order a new pcv valve for it. Engine is a 215 c.i. flathead.
Thanks for pics and best of luck with it. There is a yearly Old Threshers Reunion in Denton NC and all sorts of old tractors, parts, etc from all over the country show up. Haven't been for few years now as walking is limited. Cheers.