Blocking the heat crossover, IN the head.

Nah. Don't need it. I blocked mine and one of the best things it prevents is that dreaded Mopar crank-crank-crank no start when it's hot outside and the engine is hot. My Barracuda could literally start hot at a touch of the key. Maybe a half revolution before it lit off.

Kinda where I was at with it, the new modern design aftermarket heads don't have that cave in them.