I would mount the scoop to the motor, then with the hood out of the way i would measure from the scoop out to the perimiter of the hood opening all the way around and transfer those measurements to the hood. Then you could set the scoop on the hood at that location and trace around it to get the shape right. then start cutting and work your way up slowly and check fit often. dont forget to allow for any lip that is on the scoop base when you trace it. meaning if you trace the lip make another line inside that line to cut to so the hood will sit on that lip if you like.
I'll work on that when I get to the shop. My opening is very tight, but I have molding, so it's doesn't tear up going on & off.
I can get photo's of carbs and scoop, top & inside. It might help a little.