[63 & 64 Bowties]

This is probably the best place for exposure on these trucks.
Sorry I don't have much to offer for 58's. But, my suggestion would be to check completed items on eBay. That's what I always do. Scan other 58's and 59's to see the ones that sold, not the ones that had unrealistic starting bids and didn't sell.
Someone told me a long time ago, and I still believe it; "doesn't matter if it's real estate, cars, or baseball cards, it's only worth what someone is willing to pay for it."