Devon, the problem with New Blight and EZtec/Scientific motor blocks is two fold:
1: They are actually fairly large, the motor/gearing/electronic minimal as they are, take up alot of that 3-axle-drives wheelbase. Even if you eliminate one or two axles and keep only the drive axle there still all the inside stuff to deal with. They are about the same size practically as an Aristo FA1 block.
2: They are very VERY noisy, I used to describe the running sound of a Xmas set Scientific engine as akin to a fork in a garbage disposal. Not even prodigious lubrication helps much.
Another problem is batteries, where do you store them? Maybe in the body of the railcar, if so better to switch from the standard 6 C cells they usually require and try to use AA cells, maybe 6 to 8 but it can be held in a much smaller made-for box housing with its own on/off switch, you can get them from any decent RC radio hobby shop.