1979, 1980 machines are 8rw, lack of clean grain elev. capacity, same as 7720, also notice the lack of bubble on the right side clean grain shield. On these same machines they had a small inline injection pump, similar to 4640, and rated 200h.p., in 1981 machines recieved larger injection pump, like 8440,4840, h.p. went to 225 where it stayed through 1988.1981 machines are the first to be 12 rw ready, sorry red fans, deere was ahead along way back then,they also had the bubble on the right side elev. shield for the larger clean grain elev.1982 brought small changes, a adjustable rear h-duty axle, prior years run a fixed h-duty axle, however with the age of the machines some have been converted to 82 and newer stlye,and last about 1982 machines they had the small access door in lower unload sump, not the p.i.p that closed the larger hole on prior year machines. 1983, brought dual range cyl . drive, 1984 brought longer tail board to straw chopper, longer hoses on feederhouse for reel drive reel lift, due to different hoses on 200 series heads.Last thing about 1984, alot of people don't realize that the cleaning shoe is longer like t-2, food for thought,also 1984 machines have the larger fuel fill neck , not the red plastic covered one.1985 brought the t-2 , green cab, new stlye green tach., longer shoe , officially recognized, longer unload tube option, hardened chrome raspbars standard equipment.Also all t-2 gto a faster cleaning shoe, however most have been slowed down to 84 and older.Last thing,forgot 1983 brought harvestrak loss monitor from the factory. just alittle 20 series history. deerefever.