I have a straight 4010 1000 PTO shaft in my collection of rare John Deere tractor parts. Removed from a salvage tractor at Sikeston years ago.  Actually there was a straight 1000 option for the 435 Diesel tractors before the New Generation tractors. It’s all in the parts books for all to see. There was a Service Bulletin back in 4010 era that addressed PTO failures in tractors used with Howard Rotovators and the straight 1000 shaft was the cure.  From a 1966 price book, 4020 tractor, order code 1800 was base price “No PTO Shaft”, order code 1500 was 242.75 list price “540/1000 Dual Speed PTO Shaft”, order code 1600 was 183.00 list price “1000 Single Speed PTO Shaft”. Same codes for 2510 and 3020 tractors.