Photos no hints on what they are unless you want to spoil it don't go to this link

Inspiration- The base of an N scale Bachmann tank car. I thought it looked more like a Heavy Duty flat car so it became the following.

Yes I am aware it is upsidedown that is a glitch on the mobile platform.

Info- A paper tube (would have preferred styrene) between to "flatcars" The photos tell the rest,

I have two Athearn diesel locos that were a gift to me from my father several years ago. I have not done much with them but would like to something to improve their performance and to weather them. I know nothing about the era these diesels were put into service or how long they were used. I would like to know what the differences are in the different classifications of diesel locomotives such as a GP-2 or GP-50. Where can I go to learn about the different classifications of diesel locos?  I have attached two photos of what I have, any help would be appreciated.