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Those are the casting numbers similar to a part number. There should be a 4 digit (letter/3 number) date code on the back side. Example; A096. This means the part was cast on Jan 9 1966. The dates should be within 1-8 weeks previous to the vehicle build date. There may also be a D<N indication for Day or Night shift.

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and an ac car too ! ?? welcome !!
if they were my manifolds,...
as 052 mentioned check the dates/casting #s ,,, make sure if your "into dates" and correctness ,
that they are a matched pair they sure look to be ... nice !
then I would look at the manifolds themselves closely ,,, is the flapper moving >? how are the 4 exhaust
studs ... any repairs there ... looks like it needs 2 repairs on the passenger manifold,,, I would replace all 4
then I would have them checked for flatness,,, and surfaced if needed by your local machine shop
they can do the studs also ,,, they can grind off the flapper and just leave the rod also if the flapper has locked up
before surfaceing them at 40 -50 ea have them blasted by the machine shop and look for cracks... they like t o sometimes crack at the y ... then do the surfacing and bolt repair
probably be around 175 -200 .00 but having a quiet exhaust its worth it ,,,
do it once and its good for a long time .,,,
1 have em blasted
2 look em over good
3 surface them and new studs
4 heat em up ,,, prime them with VHT high heat primer gray when they are still hot
5 spray em with VHT HIGH HEAT cast iron gray while still warm or heat em up again

they turn out sweet ,,,,, napa should carry both paints,,,

take your bolts and other misc with you also to get blasted,,
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