For your front tire you could do what I did, smooth front sand tires in for 11 inch wheel are no longer available so I took a used Kenda front max front tire a few 5 packs of fresh razor blades and a good pair of channel locks and started shaving off the knobs I just grabbed each knob with the channel locks lightly pulled and with the other hand carefully sliced it off,don't be afraid to change blades frequently, after you get started it gets easier and the key is to leave a small amount of the knob there, after you get all the knobs shaved you will need to use an air grinder to get what little is left of the knobs off and to do the final smoothing, I also removed the tire identification from the sidewalls with the grinder, now don't get me wrong this is a lot of work but well worth it. In your case you would probably need a 110 or 200s front wheel and tire but I don't know much about the US90 and what is compatible with it, also to shave a tire it must be mounted on a wheel and inflated.
I hope this helps you if you decide to go this route, oh and here is the end result of the tire I shaved
