There are a lot of " tricks " you can do to these to facilitate cooling.
Most are laid out in the How to build Big Inch Small Block MoPar's book.
I tapped and plugged the holes going up to the heads from the ends of the deck and drilled them out to 1/8" to force more coolant up through the center of the head.
I am using a remote pump and the coolant enters the block through the center core plugs too.
I didn't mess with trying to drill between the bores , but if I was going to burn gas , I might have considered it.
This is for a dual purpose motor though......if you are not going to drive on the street or in circles , I think a lot of it is over kill.