Lower Patch Panels and Fender

[big_guy]

Does anyone know if the lower sheet metal, rear fenders and quarter panels match up body lines on a standard truck box? I have purchased a 69 GMC Panel that was sitting for a while and the bottom is totally rotten, I have a 68 Chevy long box I was going to use as a donor for replacement panels(P.S before anyone yells at me for messing up a perfectly good box there is damage on upper section and inner skin is smashed inside box lol). If it is not possible where is a good place to purchase new sheet metal? Thanks in advance for any help!