I have to agree with the dual servo's. I bought a Super Chipmunk from a guy that installed the bellcranks, and there is about 3/16 inch slop in the ailerons. I haven't flown this model yet and before I do I am going to disect the wing and convert it.

On the cowl, you might consider scuff sanding the inside and laying a layer of fiberglass. Tower carries it but you have to search for it. Go with the light stuff, not like what you get at the auto parts. Working on something with that many curves you would probably have to lay it in in small strips.

I guess the best advice anyone can give you would be to take your time, don't get in a hurry, and dry fit everything.