I don't beleave heavy flys better. I feel this plane is designed so strong it needs nothing else. As A mater of fact I used my hole saws to lighten it up and there was A lot more places it could have beed drilled to lighten it even more.
However to get into glassing this little plane can take the extra weight. I would use my own contest grade 1/16th sheeting though because the wood in the kit was very heavy to start with and if I recall right they used 3/32 for the sheeting.
I do have A friend that uses the lightest glass he can get and puts it on with {don't quote me on this} I think Minn Wax clear, not the water based stuff. It evaporates and weighs almost nothing when he is finished. Comes out looking way better then anything I have seen before. If you decide to glass it let me know and I will give you his email and he can walk you through how he does it and probably supply photos for you.
DB, I just happen to have the little Kobra on my bench right now. Building it for the same guy I built the Kav for and again for racing.
To copy the parts try using See Temp, they have A web site. Great product and easy to work with. The same builder I just mentioned sent me some of the stuff last Xmas to try and it's just too good of A product to keep to myself.