6R07mi, I didn't know you could put 351 heads on a 289. How much hp do you think it will make when you are finished with it? Can both Windsor and Cleveland fit on that engine? What about the 351 M. What does M stand for? I was told Mitzer.
Snakebit, the old Ford Muscle Parts Catalog outlines the different "stage" mods for the different engine familes,
The 351W heads are a "poor mans" GT40 head upgrade, it requires different head bolts / fasteners, matching the water ports with the intake side gaskets. HP expectations are related to compression ratio, cam selection, porting, carb etc.
If competing in vintage organizations that do not allow modern aluminum heads, only period iron heads it's one option.
The fast guys are likely cheating anyway, I don't have the big budget and wanted to build a true 60's era mod motor.
Mounting a 351 C head = Boss 302, 351M ( M=Modified ) heads are not worth messing with.
regards,
jp