I think any axle assembly without a differential will work fine. Obviously stronger is better. Since mine originated under the front end of a truck and did duty under a trailer after that the wheels have been welded into a fixed orientation 90 degrees to the axle. It'd be interesting to see if a self steering model would work (pulling from the tie rod ends or center with a welded tongue).
I've got my Logosol mill set up in the low end of a field and use shallow sloped ramps to get logs up logbed level. It works out quite well as the finished timber is already elevated and therefore easier to manipulate.
Another thing I make good use of is dry stacked concrete blocks to create pivot points and work stations for those really heavy timbers that threaten to crush my saw horses.
