Mark Dobrowolski sent me this message:

"Was looking thru your Corvette prototypes section- you have 2 cars labeled as 'XP-720'. I have been compiling all GM XP code cars for a few years now, and in material provided to me by a friend who had access to GM archives, the 4-passenger '63-style Corvette prototype was XP-796. I cannot verify this to you..., but the idea that 2 very different Corvettes had the same XP number would be HIGHLY uncommon practice."

Of course he's right, two prototypes can't have the same XP number. Since I myself had two references to this car, but none with XP numbers, I renamed the 4-seater to XP-796.

Thanks Mark!