I have a Spacewalker I had to do this to, this is how I did it.

First wash the cowl with soap and water, then detergent and water, finally clean the inside of the cowl with a degreaser or acetone(SP?).

The spacewalker's cowl is kind of flat sided so I taped a piece of mylar on the outside, card-stock and wax-paper will also work. I then laid the cowl hole side down, and from the inside laid in three layers of glass, on 3/4 oz. the others 6 oz. After the epoxy cured, I pulled off the mylar, sanded with some 220, then used some of the red stuff that comes in a big tube to fill in the small line where the patch and the old cowl meet, in my case it looked like a circle the size of the old cylinder head drawn with a pen. The just paint, mine came out perfect and was pretty easy to do.