If you had a "red" combine behind those red heads all you needed to do in order to leave 4" stumps is adjust the faceplate on the throat. We've done it more than I care for combining down corn so I know it is possible.

There is no reason a 800/900/1000 red head on a AF combine can't run as low or lower than any other combo out there. Just adjust the angle of the head and the snouts.

As for parts, I know what parts we are likely to need and keep those in the combine cab. That pretty much equates to gathering chain idler sprockets and a few assorted bolts.  Anything else that we need we have a parts head laying in the pasture that I can rob anything off that we don't have new on hand.

In the past 12 years of running a 844 IH (now a shop made 853 soon to be a shop made 882) that was worn out when it came here we have had to go to town to get parts for the corn head during harvest exactly 1 time to get a piece of 2050 chain and a connecting link.

Parts at the dealer I'd say red and green are pretty equal "here" based off of my experience but we don't get many parts through the dealer anyway. Be prepared and order what you will likely need in advance from Shoup or Sloan.