400e ?

Check to see if there is a gap at the base of the boilerfront to the boiler.  If the frame "grows" it increases in length and pushes the pivot point for the boilerfront foward.  The catch at the top pulls it tight to the top of the boiler, so the boilerfront may be tilted.  If the frame grows, it is sometimes harder to mount the motor, trucks and eventually (it could take many years) it will break.

    Besides the normal colors and type of trim, the locos came with different features through the years. Looking at it from an operator perspective a later one will run better. Earlier ones had the two position e unit which was pretty much useless, as well as drum commutators. Around 1933 these were phased out in favor of the redesigned IVES e unit and a flat face commutator. The presence of an e unit slot on top, and brush tubes on the side of the motor will show that. Also does it have a chugger? A switch inside the cab is the tell tale. Some made around 33-34 use a system similar to the O gauge 260, where they use a 3 position e unit, and have a chugger. These locos will not have an e unit slot on top, but use a semi circular slot inside the cab to control the different features. This is a nightmare to wire, so if you have extreme patience it would be ok. 

   A few other things to look for besides the boiler front gap Jon mentioned would be to check the mounts on the frame for the crosshead guides. A common failure point. There is no part besides the chugger on a 400E that is not available. 

  Just be aware that the values of mediocre originals are at rock bottom. If you look in the right places you can obtain a C6 original for around 600.00. So do not overpay! 

  Best of luck!

Jon G and Nighthawk -- Thanks very much for taking the time to reply to my questions. Both of you have provided valuable information -- always happy to learn about these beautiful toys!

Depending on how things go, I may be asking you (Nighthawk) about the right places to look for a C6 original 400e!

Thanks again -- if I make any grand discoveries or acquisitions I'll let share them here later.