2.5 in ram horn exhaust manifold identity ?

[1972k5blazer]

Could someone help ID these for me there 2.5 in ramhorns the casting number is 3797901 on both one had lh1 other has lh2 I know the generator brackets were removed from them the casting number comes back as 62-63 high hp vette but there's another number that looks like a date 5-13-91 on one 5-14-91 on the other. Am I missing something is the other number a date or something else ? Thanks just trying to get educated before I advertise them so there's no confusion. Thanks