I'm with Boyo on this--don't understand what good casting numbers are going to do u. I will note that down here in Texas all these old sixes are being wholesaled into Mexico and South America.

Not surprising that you are finding manifolds made in Mexico--they've got a load of these engines down there and are probably casting parts by now.

I had to replace my exhaust manifold about a year ago on my 250--took me a week of searching junk yards to find one. Scarce here. Assuming that the casting looks ok, hecho en Mexico wouldn't bother me at all--gonna break eventually anyway.

I think the intregal manifolds are prone to cracking and the other manifolds are prone to warpage. Key thing will it fit and seal up to the head? My 2 cents.

Buzz'n Half Dozen