Factory fenders will NOT be spliced together, they have been fixed before.
They make aftermarket fenders for these trucks. Just look thro a resto catalog like one from LMC, chevy duty, chevies of the 40's etc.
Heck even look on ebay. Aftermarket panels will need some massaging to fit correctly, as will ANY panel you buy.
The best thing would try and find some good clean rust free fenders, but for a truck that 50yr old and located in New York thats a pretty tall order. But then you would have to repair them.
So if you are trying to keep costs down, Id go with aftermarket STEEL fenders, leave the plastic for the vettes...Eric