manifold heatsink?

["Matt Howe" <ismhowe@state.me.us>]

Howdy, I've noticed on my '85 5ks that as my engine gets hotter I feel a
noticable performance reduction.  When hot, the engine vibration seems to
have a rough edge, and is a bit sluggish.  I also noticed that the intake
manifold is located directly above (and only a few inches away from) the
exhaust manifold.  As I understand it, cooler air allows for better
combustion due to higher density and therefore more Oxygen per volume.  I'm
guessing that the intake air being heated by the radiant heat from the
exaust is causing my symptoms.  Has anyone tried, or does anyone think it's
worth trying, to construct some sort of heatsink to go between them in an
attempt to dissipate some of this heat?