Thats a good writeup, and good explanation.
i ran a 36' Macdon harvest header on a 8820 for a few years, then bought a 9600, and ran it a few more years. Did not have to change anything on the feederhouse.  It was a 1991 If I remember right. It used the combine oil to run everything. It was a good header, covered a lot of acres without much repairs.
It was a vast improvement over a 930 auger head. I could never get the 930 to feed smooth in Durum wheat, it always fed in wads. Running the Macdon was a little bit of heaven.
Now have a 36' 974 flexdraper on a 9760sts. Many improvements over the old header, but most likely way too heavy for a 8820.