I'm looking at a Dynaflite chipmunk, the same as yours. ARF's are ok, but you can't beat a built up kit, the ability to reinforce if needed and to personalize it more.

So if the firewall is 4.5" with 3/4" of an inch on either side that you saying the width of the cowl is 4.5" + 1.5" -> 6".

I just measured my OS FT160 twin and it's 7.5", looks like the valve covers would have to stick out or I could just get a Saito 180 for it. Either way I like the look of the it and if I get one it definately would have to be in RCAF colors.

Dave
AB, Canada