Yeah quite scarce and interesting.
The most interesting part for me is GMH stopped trading their parts and accessory division as NASCO around 1973.
Appears they continued to use the NASCO codes on bodies and replacement engines longer.

I did know a bloke who purchased a brand new WB Panel Van shell although I never did bother to study the tag.
I assume most who still had their original tags on a damaged body would have just swapped them over to the new body.