What style of trucks would have been used on this prototype crane? 120-Ton Brownhoist Railroad Wrecking Crane and is there an aftermarket version of the truck that would work?

I am very interested in building whimsical "critter" engines and rolling stock on a small layout, preferably HO gage.
The problem is, I cannot find where to purchase the small motor drive on a just two axle truck assembly on which to build. I would very much  appreciate any help and advice.
Happy new year to all.
Tom

Hi All, I have started posting here after reading for a while, and I thought I should introduce myself and share where I am at and what I am working on at the moment. I am a PhD Student who is living in Hungary, but is originally from New Zealand. I am just starting to seriously get back into the hobby, though as a teenager I was very keen on model railways (I'm 32 now). Because of my research I will be moving a lot over the next couple of years so right now I won't be starting work on a layout and will be limiting myself to some more manageable projects.

Seems like a lot of people are having trouble with electrons.  In particular with the electrons in DCC circuits.  However this doesn’t preclude a number of people who are using DC circuits. 

DCC complicates diagnosis of electrical problems.  A simple device can go a long way at finding a trouble spot in track, switches, motors and on and on.