only differences in '84 and older models are reverser, cleaning fan shroud, elec. display in cab, longer sieves, heavy rear axle.The last thing is a must on all and may have already been changed. I beleive you will have machine width issues on the 8820 with a 6 row head. Their is nothing wrong with any of the older models, everyone thinks having yellow paint on the cab roof is a big deal, but it only makes it cost more. I ran a 6620 in up to 240 bu. corn for 18 years and it never had a problem getting it all in the bin. JMHO.. gs