I may be operating from faulty memory, but it seems to me that the later core supports had much smaller holes and the 66 and later supports had no headlight holes, at least on the 100-200 series trucks.
Learned something new today. 61 core supports had holes. 62 and later are just dimpled, as seen in Norm's photo, except 62-65 has 2 dimples. Went out to the herd and confirmed it. Haven't ever parted out a 61, so hadn't made this observation until now.
Cool what Steve taught us all by posting that pic...