1. No approved option for such a conversion. Would be cost prohibitive it was - new wheels, tires, etc. Work with what you have.
2. The buyer could buy solid pneuamtic style tires - best long term choice.
3. Yes, air type pneuamtic tires can be foam filled - but you need to find out what the total cost will be, plus the truck will be down for some time as the foam filling must requires a curing time & usually this cannot be done on site. A limit to foam filling is if there is a cut in the tire (liek a side wall cut teh foam will escape).
Contact a local industrial tire company to help you with this project.
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