Nishijin A - what is this part called

[prdycool]

Hello! I'm new to pachinko - my goal is to restore my MIL's old machine to working condition. I've done some cleaning and identified it as a Nishijin model A (green parts). The biggest issues I've noticed are a missing nail or pin to hold the jackpot tray and it is missing the spring loaded (metal?) door over the track just before the jackpot tray. Based on a video, the purpose is to keep the balls only one layer thick. What is this piece called? Is it absolutely necessary for functionality? Where might I look for a replacement?

20210406_093550.jpg

Thanks!