What you say about front wheel bushings makes a lot of sense when I consider the clip holding the wheel on. I do not understand why the designer would use a bushing instead of bearings. I have only seen this once before on a consumer grade trailer for a lawn tractor. Do you have any more info on what bearings you used? Considering the way the wheel is made, I am assuming they were needle bearings-am I correct? Do you know what size they were?
As to tire pressures, the front tires have nothing on the sidewall of the tire. The new rear tires only have a maximum air pressure of 35psi. This is what I would put in a van that would weigh 2800 lbs. empty and maybe up to 3500 lbs. when loaded. I recall the Elec-Trac weighs about 700-800 lbs. plus about 175 lbs. for operator means a gross weight of less than 1000 lbs. I expect I will have to do some rough calculations and experiment.
Thanks for the feedback.