Brilliant idea to use the top of an old case. This is similar to the business card that is now being designed.
The reverse side, the actual top, of this case has silly string all over it otherwise, it might be the
best side to use. I may try to scrape it off tomorrow and see if paint will cover a multitude of sins.
The solution may be to create a larger guitar top. Not sure I'm up for this.
I do have a base case and it might afford a larger surface. Running diagonally, for
instance. Will test tomorrow.