Yeah, you gotta pull the rockers but that is nothing compared to the manifolds.
Manifold gasket may still be OK but no guarantees. I put a thin layer of
grease on mine and it keeps them from sticking so bad.

I forgot - how are the rings in this engine? If it is just valve guides and
you replaced them it should help. When you get the head off look closely at
the cylinders and the tops of the pistons for indications of problems.

What makes an engine run hot or cool is all in the radiator and the air that
flows through it. There is plenty of room around the engine and the firewall
for the air to escape out the bottom (unless you have a belly pan). Leaving
the hood loose at the front is a definite hazard, and at the rear you never
know what might come outta there and get on your windshield.

BTW do you have a fan shroud? or do you just have an electric fan?
--
George Downs, Bartlesville, Oklahoma, Central US