:Stop:
Don't do it! At the very least, one of your rear tires will seem to be constantly off the ground on the leastest unlevelest of conditions. This will majorly stress out your frame, leading to premature failure.
The reason for this is when you have a pivoting front axle, essentially you have a tricycle. Three points will ALWAYS lie in the same plane (triangulation, if you will). Four points (4 tires always in the same relationship to each other) will also always pretty much be in the same plane, so you better hope the ground you're working on is perfecly flat, or the two planes will never be parallel. Long story short, this will spell early destruction for your frame or front spindles, since they will no longer equally share an uneven load either from forces in the loaded bucket or those on the ground.
Think: camera tripod vs. 4 legged plastic molded outdoor chair placed on hard, uneven ground. Which is more stable?