I've done it. Just take a 1" thick tape carefully placed on the outer black.

Cut very carefully with a hand powered jig saw.

I cruise a 3200 rpm. With blasts up to 5000 rpm. And take it out to the road course track to close to 6000 rpm.

No problems in 8000 miles since built a few years ago.

Really reduces the effectiveness of the fan though. But less drag. I have a custom built shroud, run the Jag fan clutch, use straight water with additives, block meticulously cleaned of debris, and 4 core Champion radiator. No cooling issues.