here's what I did...
got a long straight edge and a tape measure. pop the hood, and lay the straight edge across the top of the fenders, and line it up with the stud for the air cleaner. mark the fenders where the straight edge is. then I took a measurement from the square edge on the inside of the fenders (the edge where the fender bolts are) to the air cleaner stud.
drop the hood, match the straight edge up with your marks on the fenders, and using the fender to stud measurements, draw a mark where it all lines up. there's the center. I used a light tap on a center punch to mark it, and then a........
I'm totally drawing a blank as to the name of the tool I'm thinkin of. compass? that doesn't sound right. you see it in art class... it's an adjustable "V" shape, with a point on one end, and a pencil on the other.
anyways%) ...
use that to draw the circle on your hood (in the appropriate diameter) and then cut it out with a sawzall. you do need to cut through some of the hood support...I used rivets to secure them to the hood after the hole was cut. bevel the cut edges real quick with a grinder, clean it, paint it...done.