I guarantee you will be happy with their products. If you want a complete kit with with huge improvements in sample, capacity, and fuel consuption get these parts from Precision- High perf feed accelerator and discharge beater, discharge beater speed-up kit, element kit, concaves, white cap bar, adjustable precleaner, 20% power chip. 300 acre money back guarantee. If you only do some of the upgrades you will find the unimproved areas will choke the machine down. Trust me.
The whitecap bar bolts to the rotor frame rail on the right side just above the stationary concave support tube. It's right where the concave latches are. It blocks material from exiting the rotor and falling into the conveyor augers, including whole unthreshed heads. Why Deere chose to overlook this large gap is beyond me. Precision charges $45 for it but you could make your own pretty easily with a piece of 3/8 by 1" flat steel. Just make sure it doesn't interfere with concave movement and removal. They don't mention it on the website because it's such a simple thing.