Jim --
SN is stamped (lightly) on a flat spot on the block just below the head on left side near oil filter. Your description sounds like it's not an 8N but it could be a 2N.
The biggest differences with an 8N is they don't have the Furguson System badge, they do have a four speed trans. and have two hydraulic controls (draft and position.) There are other differences, but it sounds like yours is not an 8.
9 vs. 2 is trickier. Pre-war 9s have an I-beam style radius rod. 1939 and 1940 used a four spoke steering wheel, but wheels are frequently replaced. 1939 had an aluminum hood and grille (rare.) Early 9s had smooth hub axle shafts, 2N has riveted hubs, but.... the smooth axle shafts tended to break and were replaced over the years with riveted ones.
The best thing is to lift the SN, then look up the year for that number. Then go back to the tractor and try to disprove the SN by looking at clues like the ones mentioned above -- if you can't disprove the SN year then it's probably right. If you do find something inconsistent then you're left with a dilemma of whether or not it's a different engine in your tractor or a replacement part on an otherwise straight tractor. In the end one may never know 100 %
Hope this helps,
Pete P.
Harborcreek, Penna.