Hi Rick,
I think the key you're referring to is Q-451. Looks like from the parts drawing that the bent up ends are done so the key rides side to side with gear 341-033 on shaft Q-482. The middle portion should fit in gear 341-033 with a bend up on either side of the gear. That gear is attached to the QCGB sliding selector lever so I'm pretty sure the key moves with the gear. I'll take a peek at mine and see if it's visible to confirm I'm picturing the assembly correctly from the parts prints. You should be able to put the key stock in a vise clamped against a piece of stock slightly wider than the gear; hammer each end over and clean up with a file.
I've read other strings and seen ads for machines on eBay with a tooth broken out of the back gear. Didn't seem to cause a lot of problems, but do you fix it with the lathe already torn down? Personally, I'd weigh the cost of a replacement gear vs. how much I plan on using back gears. If you're going to do a lot of single point threading with heavy cuts, probably look at replacing the gear. If you don't fix it, I'd be careful changing chucks if you lock the spindle by engaging back gears without pulling the spindle lock pin. Make sure you have full teeth engaged and not the gap in your back gear. You could paint a witness mark on the shaft and/or gear that'd stand out when you lift the cover over the headstock, just turn the spindle by hand to make sure you're on full teeth when changing a chuck.
By the way, my lathe is serial# 2215, just a few hundred after your lathe. They should be really close if you need me to look at anything else. Mine is a "stripped" model; 2 1/4" x 8 threaded spindle (not L00), no clutch, no varible speed drive. I do a deep knee bend to flip the lever on the floor to lift the motor and move the drive belt to change speeds. Do most of my turning at 650 RPM as a result. Regardless, it's a really nice lathe. Should make you lots and lots of chips with no hiccups. I wish I had the taper attachment like yours!
Best regards, Bruce