I'd like to create a 3D guitar cake, which will be propped to stand at an angle using an acrylic cookbook stand. My question is, what will be the best way to create the neck of the guitar, so that it can be attached to the cake, not weigh too much, and not pull the cake apart? Thank you so much for all of your help!!

I would use RKT for the neck of the guitar. And I would just run a dowel through the cake and the neck of the guitar, for stablity.

I agree with the RKT. However, I have done a guitar and make it out of cake. I secured it to the under board with RI and it held tight, but I don't know how long it was at an agled position.

I made mine out of styrofoam and covered in fondant, it worked great.