I've seen (and posted) several trucks with similar conversions, including window decals - I just don't know what company did the conversions:
http://www.ebay.com/itm/1963-Chevy-...3f0e56&item=251511377494&pt=Commercial_Trucks
http://www.ebay.com/itm/1963-Chevy-...3f0e56&item=251511377494&pt=Commercial_Trucks