I built a balsa cowl for my .40 sized Lucky Stick, which was just an ARC version of the Ugly Stick, and it really isn't that hard to do!

Start by making a circular nose ring out of 1/8" light ply, the same diameter as the spinner you want to use (you can use your kids compass to draw the perfect circle if you have one, or just use the spinner backplate as the template). Just don't try to use TOO small of a spinner!

Cut the center hole out of this nose ring plenty large enough for the engine prop drive washer to fit through. Now tack glue the nose ring to the back side of your spinner (I use SMALL drops of CA for this step) with 3 or 4 SMALL pieces of 1/16" balsa stand-off pieces (this will give the uniform gap between the front of the cowl and the back of the spinner). Make sure the nose ring is exactly centered on the back of the spinner.

Now, with the engine mounted to the plane, attach the spinner securely to the front of the engine with all washes, and drive hubs etc in place. The next steps are the fun parts!

Using something like 1/4" (or thicker if you have it) sheet balsa, start carefully cutting and gluing pieces of balsa (grain lengthwise) between the firewall and the backside of the nose ring such that the planks outside edge is always glued either flush with, or slightly outside of the outer radius of the nose ring and also the fuselage sides at the firewall. It takes a bit of time and patience, but keep cutting and fitting the balsa slabs (they will have to be tapered in width as they extend from the firewall to the nose ring) between the firewall and the nose ring, until you have all the space filled in between the firewall and nose ring below and on each side of the engine. It will look ugly at this point, by have a bit more patience, as you are getting closer!

Now take a sharp, fine bladed exacto knife and slice through each one of the 1/16" balsa pieces holding the spinner to the wood nose ring you made. Next remove the spinner from the engine, and then the engine from the plane(you didn't cowl the engine in so tightly that you can't remove it did you???). With the spinner and engine removed, you now just need to take out a sanding bar with relatively coarse sandpaper and start sanding the contours of the balsa cowl to blend all the sides from flush with the fuselage at the firewall, to the exact roundness and flush with the nose ring outside diameter. Just be careful NOT to sand into the nose ring with the sanding bar/block, or your cowl will not be perfectly round where it meets the back of the spinner!

Once you have the balsa planks rough shapped, you can reduce the grit size of the sandpaper to achieve the nice smooth contours you are looking for. If you find that you start to sand through any of the balsa planks/blocks at any point, small pieces of balsa can be glued quickly into place (use CA) to build up the INSIDE thickness of the cowl, before sanding any further. Once you are satified with your contours and smoothness, you can re-install the engine and spinner and do a final check for fit. You may have to slightly enlarge the opening inside the nose ring to slip the engine through, and you may also need to use a dremmel to carefully remove a little balsa from the inside of the cowl if you added some during shaping/sanding and it now hits the engine.

Once satified, remove the engine and paint the whole inside and outside of the balsa cowl with thinned epoxy to fuel proof it. Once it has dried completely, give the outside a final light sanding and cover with your choice of iron on film (you will need to use several pieces and work from the firewall forward). Just make sure that you leave at least 1/8" of covering to iron over onto the flat face of the nose ring so that the covering does not start to peel back when you fly the plane.

Now re-install the engine and go show all your friends!

I'll try to attach a few pics of my Stick so you can see the final result. I called mine the "Slick Stick" as I think the cowl really does "clean up" the designs aerodynamics a lot!!