Blocking the heat crossover, IN the head.

If you plan on street driving it at ALL I would leave that passage open.

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.