Yeah (so much for me saying I'd bet it's close to the 400 series single pedal HA lol!) that should be the adjustment for the angle of the beater which gives you quite a bit of settings and fine tuning adjustments. You can tighten down or loosen that tension adjuster that's attached to the spring and then when you loosen that screw that I showed you, you can move the beater back and forth, at least I think you'll be able to. Cause yeah the beater is quite close to the bass drum head and now I know why you are so hung up on the maximum possible distance when the tension is at max. In order to get a bit more distance you'll have to loosen that screw and pull the beater back toward you. As for a standard drum key, can't be more than a couple dollars? Here you go, a two pack for $7 just incase you misplace one. Best to always have more than one cause they get away from ya lol!
http://www.guitarcenter.com/Sound-Percussion-Drum-Key--2-Pack-105766208-i1502821.gc
Also yeah no problem, we were all noobs at one point, I'm glad to help in any way that I can even though I'm an 8 month old noob as well with 3 years prior experience when I was about 14 or so lol! Also those PDP's look to be in great condition, the wood inside looks well taken care of as well as the wrap and hardware! I'd say clean them up, build upon them and enjoy while learning! Learn to tune them, play, different ways to set up etc. Very cool to see another PDP player!