blown 2 head gaskets

can be fuel starvation
but both time a the same place??? hummmmmmmmmmmmm

of course the heads gasket are the fuse in your situation
its the cheapest links in your engine

for fuel delivery for sure the blue pump arent the best choice
but I ran about the same set up as yours with the same pump
and I change mine for the black one but no need
to go biger and bigger pump if the line are too small
or the fuel pick up in the tank still the OE 5/16

you can buy the 1/2 from mancini or else where its pretty cheap
I made fuel line with russel 5/8 hose I install 2 fuel regulator
one set 8 psi for the carbs and the other at 5 psi for the nitrous
why 5 more than that my nitrous systeme were to fat
but Im using a nitrous work kit and they are that way as said
by there tech when I called them to answer to all my question