[GaoMuscle Longhorn]

I'm going to go wild and use locomotives from around the globe.

Red: A Shinkansen
Blue: British Rails Class 55 Deltic
Green: Swedish Crocodile (or, it that one's too big, the Rhaetian in Green)
White: Santa Fe Warbonnet-like 1950s A Unit
Black: Pennsylvania Railways GG1 class (In a GaoBison full-legs type deal)
Yellow: A Thomas The Tank Engine era Steam locomotive, with the Tender being a weapon

For others:
Sixth Ranger: Some type of Garratt locomotive, and a damn big one.
Bragigas-type Mecha: Union Pacific Big Boy

Second mecha: an Armored Train
Possible freight cars in a Shinkenger-like weapon add-on set?