I will, of course, inundate you with Challenger photos in a minute. These are copyrighted photos, and you may use them with my permission anywhere but in this thread.
There are a couple of thread participants who know the history better than I - but here are the few things I know. The Fetters, or "baby" Challengers were modeled by Lobaugh only prior to WWII. They were not produced after the war. The 1950s version was the larger "Jabelmann" Challenger.
These early models came in several flavors - major difference was in the way the geared axle got inserted into the frame. All of the frames I have messed with get modified so that all axles drop out the bottom, just like the real thing. I am not familiar with prewar gearbox variances, but can tell you that Raoul's NWSL Mod O.6 non-tower gearboxes are the cure for all Challenger gear problems. The huge open frame AC-DC motors can be replaced with Pittmans easily, although about half my Challengers have original gears and motors. They do just fine, at six amps.
Lobaugh also produced a D&H Challenger and an NP Challenger, all based on the Fetters parts. My D&H is an original, but it came with damage, and USH gearboxes. New frames, some body work, and a little attention to detail and I had at least an original locomotive. The Lobaugh tender is not accurate, so I junked it and started over, using only trucks and underframe.