Looks like the new manifolds have beefed up bolt bosses.
The originals and the older reproductions looked like they were thin in that area.
Pop's was having their version made overseas. But I never heard of any issues with their exhaust manifolds.
One of the factors in producing something like this is the quality of the cast iron. Ford learned that difficult lesson in the late 80's fuelie 302 and 351W pickup - those manifolds would fall apart in multiple pieces when they were removed from the trucks. Dealers had piles of them. Clusterfluck to R&R because of rusted bolts. Probably the originating factor was increased operating temperature from the fuel injection and emissions. Ford had to go to a better material, I think it had increased silicone.
