If I design one, I'll make to fit onto a $15 Harbor Freight furniture dolly. Cheaper than buying caster wheels, and can be set in a truck bed without the wheels for stability.
I haven't had success going that route. I built six dollies using the Harbor Freight 1000# furniture dollies. There are two problems. The first is the casters, they are too small in diameter and of poor quality. With the weight of a fully dressed out 440 you can barely move it as they catch on every minor defect in the floor. After you have moved them around for a while, loaded all the time, the casters start deteriorating making it harder to push. The second is the dolly itself, I made a box on top of the dolly that the oil pan fits into. Even with this additional reinforcement, with the constant load of an engine the dolly starts to sag.
The next one is going to be steel square tube and at least 3" diameter casters.
