Hello and welcome to the forums. is the bike complete except for tires? or is it just the frame? if you or your grandson can post some pics we can give him some idea of if it is something worth trying to sell as is or would need repair before being sellable.
personnally I have no idea what a Silver King is.
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“One morning you wake up, the girl is gone, the bikes are gone, all that's left behind is a pair of old tires and a tube of tubular glue, all squeezed out"
Sugar "Kane" Kowalczyk