Howdy! Here is a method to make any radial type cowl you want. The first pics shows the blue foam 'bread and butter' glued together. Now you can hand sand everything from here to match the template shape and diameter of the cowl. That's it! Now just cover the foam with water based glue to seal it and glass it, sand some more, add filler, sand some more until you are finished. Dig/ melt out the foam. Cit opening(s). Primer and paint. Not difficult but takes time.

I have used a hot wire set up to save a little time. I also pull a mold from these plugs anymore in order to make another cowl in case of mishaps *wink*. The epoxy is only near the center to keep from creating hard spots that will screw up the hot wire process. A simple 'lathe' is made from wood, dowel and hardware store bearings. You can see the template made of cardboard. A buddy helps with turning the cowl while I cut with hot wire. I used the hot wire as much as possible to save time hand sanding. There are books on the process and your first endeavors will be fun because it usually works! The last 2 pics show cowl after being sanded very smooth and covered with, in this case, DAP brand Lightweight Spackling' which is the same as the hobby store stuff. For this cowl I'm 'sealing' it with Minwax Polycrylic and then glassing with 'Bondo' brand polyester resin and glass. It is for a 1/4 DH-5 and is 11 1/4" diameter. I like epoxy but it is expensive and creates allergy issues. I wear charcoal filter masks doing all of this. I always wear safety glasses.

To make non- radial cowls bread and butter foam from spinner to fuse join(if needed) and make templates of top view, side view, fuse join and spinner backplate (usually round). Cut with bandsaw the top and side views nesting part in off cuts for each subsequent cut. Now, start sanding! Finish as above. Takes time but doable.

If you already have a part then 'slick' it up (paint, etc before cutting holes in it), wax it and pull a mold off it. Any ??? and I'll try to help. Good luck! ARUP