To the best of my knowledge, the last ones they made had extra material added for porting........ over and above the earlier MP ones........ that had extra material added for porting.

They sure seem quite a bit heavier than the oe ones that came on production 426’s when you’re moving them around in the shop.

68 Satellite, 383 with stock 906’s, 3550lbs, 11.18@123
Dealer for Comp Cams/Indy Heads