Blocking the heat crossover, IN the head.

I would think it would be much easier "in" the intake, and less dangerous.

Intakes are generally cheaper so if you screw it up.............

You are not looking at something falling down into the valves.

Just some random thoughts, I've never done this.........completely clean the intake, grind the crossover into virgin material, and either braze a plug into an iron intake, or tig an aluminum plug into an aluminum intake.

I've actually considered doing so.

I've also simply considered completely filling the crossover with hi temp silicone LOL