wulfie14,
do you know what the difference was between the A-4 > A-5 > A-6? - to much for any field conversion. If there was 3200 A-6 built, thats how many there was, no more, no less.
An example of a re-build is the NASM's F-8 (WkN 931 884) which had an A-7 ID plate (WkN 640 069), found during restoration, still mounted in the fuselage.