To get the prop flange in the center of the existing
hole I need some cowl measurements.

Place the cowl sitting on the floor in the corner of a room and
and measure the distance to the center of the hole. The
floor represents the firewall.

Then measure the hole diameter. I assume the hole is in the center
of the spinner location.

Also measure the height of the cowl so the prop flange
comes out nearly flush.

The other thing I need is the down thrust and side thrust angles.
Those numbers should be in the plans.

BTW If you don't have a cowl and need to make one it is always a
good idea to use a 16 or 18 inch spinner with the rotary as that
gives more useful volume in the cowl.

Paul Lamar