David

Did you use a new case?   A pounded case will transfer 20% of engine output
into heating the engine.
A 'line bore' will not make a pounded case good.
Most line bore tools are the bar type and just make begger holes in the case.
 If the case was so whooped on to start with you have an incorect starting
point for the machine work.  If the axis of rotation of the crankshaft is not
in line and angled up correctly to the piston cylinders then that engine will
never have the output and will always overheat.
That melling while a fine peice of machine work is no good.  The iron
casting's rate of thermal expansion does not match the Mag-Al alloy of the
case, so when your engine is warm oil leaks back into the sump from the high
pressure side.   It could also suck bubbles of air in on the intake side.
also the pressure can go way too high with a melling, too much is too much.
 You could have so much pressure that the stock relief valve will bypass the
cooler even with a hot engine.
The stock pumps work fine, if you must get one from berg, they are stock but
the alluminum has been treated (anodized) to make the surface harder/wear
better.