The "N" models were grey, the 600 series were red and it was after them Ford used Blue but the updraft carb I do not think was used when they left the 600 and 800 series models were stopped and they went to the 3000, 4000 and so fort models. I believe you are working with either an 8 or 9 N but could be wrong. Look and see if you can find a serial number and if you do see it tractordata.com has serial number like yours in any of those models.
As to getting the tractor idle those updraft carbs at least one our 601 are touchy. Last I know NAPA had those carbs but that was over 20 years ago. I would get the tractor running at lowest rpm it will and slowly adjust one (of if memory is correct there are only two screws to adjust) screw slowly at the time. I would turn say 1/2 a turn and let it run for few seconds to stabilize and then do it again.
Are you sure the throttle linkage is letting the carb return to idle? If you have not remove the linkage and be sure you have full travel of the butterfly in the carb.