If you have the header, off the raddle chain isn't too hard to get at via an access door below the feederhouse (when the feeder house is in the raised position). On an Gleaner E the raddle design uses implement chain and wooden slats. EIII is the same (I have one).
If you loosen the chain adjusters and can use an implement chain tool to take links apart on each side then it's not to difficult to get out at that point I would think. The weak link is the wooden slats, corn in particular is hard on them and you'll find most running E's with some missing wooden slats from breaking. They were riveted in at the factory so while you can make new slats (not sure if AGCO still sells them), it's more of a pain to rivet them back in while the raddle is still in the machine. I don't know if AGCO still sells whole new raddle chains. I'm sure they'd be pricy if they did.
On the K, they went to a CA550 roller chain raddle and thus it uses different sprockets. You can upgrade the E I believe to the newer K sprockets and buy a K raddle to replace it but you'll probably spend $1K for the new roller chain raddle and sprockets. The sprockets I believe would be a bit of a project to replace. Abeline Machine sells raddle's for K's, about $440 plus shipping. Mike