The pro-topline thread in the Product forum got me wondering, especially after seeing this pic:

The Pro head on the left is taller due to the deck height. Folks in that forum mentioned that you can mill the head to get very small combustion chamber sizes.

But... the difference in height is staggering. Assuming that the heads are made to be a bolt-on in their unmodified form, how much can you mill off before you have fitment problems with intake manifolds and headers?

I just can't get over the massive difference in height. There's got to be at least a half-inch difference, and there's no way you can mill anywhere near that much off the deck. To me it looks like all of the additional height is above the upper accessory bolt hole in the head. The valve springs appear to be at about the same position, but the valve cover perch on the Pro heads is a mile higher.

 

Looks to me like it wouldn't effect the intake manifold at all, just the height of the valve covers so everything should be fine.

 

The extra height is from the raised rail design of most aftermarket heads to better seal the valve covers. As stated it only effect the height of the valve covers.