Axle suggestions?

[frizzen]

I'm looking for some possible axle suggestions to power an old steel earth moving toy, that i will be able to reconfigure for either Dump or Scrape operation. This is a Power Unit of something 2 axle and articulated. Basically it's an offroad tractor with permanent hitched attachment and no front axle.

The bigger setup 'just as a toy' empty weighs in around 11 lb 6 oz (11.5 Pounds). It's also going to need to be able to drag around a 'pretty good chunk of dirt'. One config has a tapered hopper 6x11.5x5", the other i'm not sure how to actually measure bowl struck or heaped capacity, so let's say 7x6x4" and self loading. Moving some yardage.

I'm thinking it's probably going to need some type of Crawler axle or Gearmotors?

Tires are 4-3/16" tall. 1-1/2" wide
Width between frame rails 2-7/8"
Frame rails 1" tall,
Fenders come out to 5-1/2" wide

I could probably either run each wheel tank-style, or come up with a way to steer off the trailer gooseneck.
If a crawler axle is the best way, a locking-diff would probably help to be able to swing around and still dig in?