GT40 iron exhuast bowl and thermactor hole

i'd check for ya bro but my 95 gt40's still have the valves seated

Not sure what you are asking here.

Based on my collection of heads, inlcuding some 94 Lightning units, they have the air injection ports from the exhaust bowls to the back of the heads, and the exhaust crossover passages that allow exhaust to warm the intake. These are two separate functions. The small bump with the hole leading to the passage to the ends of each head is air injection system, mean to carry air from the smog pump to the exhaust ports to facilitate complete combustion.

As far as I know, yes, you can block of the "heat riser" passages from the exhaust to the intake, and it is ok to grind out the "thermactor bumps" in the exhaust ports smooth with the port roof.