Well, I think YOU need to get out of the hooch and re-read my post with a clear head! I haven't seen any 6620 in my area with 6 row heads. Most guys that still have that combine have 4 row. Also most 6620 here are Sidehill models and much heavier than an F, which takes more power and causes more compaction. To put a 6 row head on an F, you fill the rear tires with fluid and put donut weights on the wheels. The l and M had an option of "fat back" wheels, which was a solid cast wheel_hub in leiu of a steel rim. I'm not sure if that was available for the F. Putting a washer under the slip clutch spring goes a long way to solving the clean grain capacity issue. Several 94xx and even 95xx model JD with 4 row heads here. I don't know how they get thru the field without knocking down the adjoining rows. The ground is yellow behind them because they probably aren't running full or at least are not set properly. I bale stalks and see what gets left behind many different combines. The John Deere's have the most grain on the ground - I don't know if it's the combine's fault or if it's just that the JD operators don't care.