Post a picture of your 964.

[mcgc0]

Not sure if that would help cooling but I think this car was a full on lightweight project so holes were everywhere!

To aid additional cooling you would need to physically cut out the rear of the body and heat shielding that sits behind. The grille essentially replaces the whole length of the reflector panel and nothing more.

 

[Hacki]

Engine cooling has never been a problem with my 964s (all normally aspirated) in all those years; neither on the road nor on track. Not even on tracks like the old Hockenheim on a real hot day. When the 964 was raced in the Carrera Cup (rules were very strictly controlled) some racers tried to keep the engine lid a tad more open - not for cooling, but for more fresh air.

A 964 is pretty much bulletproof as it is. Brakes can be an issue in case you want to track it, especially the two-pot rears of the early C2.

A lightweight project is good fun (and helpful), but drilling all these holes won´t probably help, it seems to have a more or less psychological effect. I have seen a car with drilled doorhandles - leaving your watch at home saves a lot more weight I guess. But hey, nothing wrong with living your personal dreams.