What is a "Raised Port Style Manifold"?

I am going to copy & paste a selection from the Summit website about GMPP Fast Burn Cylinder Heads.

Fast burn for high performance.
These fully assembled, CNC-machined aluminum Fast Burn cylinder heads from GM Performance are designed for 1958-2000 283-400 c.i.d. Chevy V8s. They quickly and completely burn the air/fuel mixture, ensuring higher cylinder pressure and more power. No additional porting is required--GM Performance Parts' cast-ported technology gives these heads maximum performance right out of the box. They're drilled and tapped for Vortec and raised port manifolds, they accept flange-mount or centerbolt-style valve covers, and will support in excess of 500 HP.

 

Raised port = Vortec

Vortec is just GM's marketing name for "raised ports"

Those heads require a manifold with the Vortec type ports. The top of the port is about 1/4" higher up toward the valve cover flange. An older manifold won't even cover the whole intake port, and even if you happen to have one with unusually thick casting across the top such that it at least touches the top of the gasket hole, it will certainly match so poorly that it will throw away the $1100 value of the heads.