FWIW, on my 77 930 I did something similar, but drilled five 2" holes in the horizontal removable piece below the rear reflector "box" and the five more 3" holes in the rear sheet metal to vent the heat from the turbo. I fitted stainless mesh behind the holes for a more finished look. Before doing this, I cooked part of my rear fiberglass bumper. The heat that moved through the holes did not enter the engine compartment.
