Why not just buy this cab as a starting point? They are only asking $300... Wouldn't be too bad to ship it likely. https://www.facebook.com/marketplace/item/159436635979115/?ref=search&referral_code=undefined
I have a mate here in NZ who owns two sets of genuine C Cab panels, new old stock, never been assembled. I believe he would sell one set. I tried to call him but got a cryptic MIA message on his phone, will try to see him over the weekend, get his new number for you. Try Castlemaine Rod Shop , before Kelvin Waddington and sons bought Castlemaine they used to make complete new early Ford pickup cabs at Waddingtons Street Rods.
I will correct that he has an original set of C cab panels and a new reproduction set. He is willing to measure/photograph/ draw the panels , whatever High Test 63 needs . He can also explain where the repro panels are available from. I will PM High Test 63 with John's contact details.