I used light weight caster on a Pontiac V8 test stand I built. They were strong enough to hold the weight with even a little extra strength. Once the engine was loaded, it rolled OK till it hit the bump leading out of the garage. Two of them bent and stopped. The shock of the bump was enough to trash them. The next set was double the weight capacity of the first set, they have been working fine so far.
As long as your floor is super smooth, you can get by with lighter wheels, but if you have a rough floor, go twice or more of the total weight. Wider is also better.
