I don't think I've ever seen those manifolds before. I've owned a '65 Coronet 500 that was originally equipped with a 426S for a long time but the original engine was gone when I bought the car. It had headers on it and a Max Wedge cross ram when I bought the car. I swapped in later model HP manifolds but those original manifolds would probably work okay. Maybe give up a little power to the later HP manifolds.

I always considered the factory 426S to be a dog of an engine. The cast iron intake is low profile and it didn't have much of a cam. More of an executive cruiser car than hot rodder setup. But as I get older I'm probably more in tune with an original 426S than the hot rod engines that I've been using. Maybe I'll go ahead and return my '65 to its roots someday. Who knows, maybe I'll be happy with 365 hp rather than 575?