Yes, the cobs on the walkers are almost all whole and the cob screens are working great.
According to the OM I have, F2 SN<46000, my current belt+pulley combination is as slow as it gets. The pulley is the largest one they made for the F2 at 20in, which has a speed range between approx. 410-680rpm. They had a chain drive option for the cylinder, which could go down to 175rpm, but the combine didn't come with that and I think that is too slow anyway.
The cylinder bars are good, I turned them earlier this year before doing small grains......and no, I do *not* have the cylinder lap bars, or "filler plates", the guy I bought the combine from didn't have them. The OM suggests adding the filler plates when you cannot get complete shelling, while trying to run whole cobs, within the suggested RPM range, 400-700 and cylinder clearance of 3/4in.
Went back to 3/4in this morning per your suggestion, also tried 7/8in, with a variety of ground speeds in 2nd gear. Still about the same for damage regardless, 5.5-6.5%.