I believe you are very correct, he apparently was not building replicas but doing complete rebodies on old chassis. The article in Carrozzeria is not clear on that point, it speaks to his "recreations" but only in the sense of the bodies themselves.
I first became interested in his work after accidentially bumbling into his place in upper NH in 1993 I think. There was a pretty much complete 718 body in old racing paint sitting in the front, behind a big glass window. I thought I had found the holy grail out in the weeds of NH. Boy, was I surprised when I chased Joe down. Not only did he know the cars front to back but he was making a copy of the body in the shop. Like you say, even then he had some bucks to kill for....550's, 550a's, and maybe even a "D" Jag as I think back.
In any even, an absolutely great craftsman who continues work today...