No clearance issues, unless he's talking about putting set screws in the head and not going flush on them, to block the exhaust air pump feed passages that sit about a half of an inch down on the head from the exhaust ports. Or maybe a set of the '302 head exhaust manifolds?
Aside from the air feed passages, externally they have the same dimensions and if you go flush with the set screws, you don't need to worry about any clearance issues with your current exhaust.
The exhaust ports and intake ports are standard 318 size and alignment, as well as the bolt holes, water passages and oil passages.
Basically, just block the air injection passages below the exhaust and go for it.
