Hi steve , yes they do move, and yes they can shrink a tiny amount e.g. 1mm . For electrics I am not very knowledgeable. But if you can look at a famous spanish guitar maker named Ignacio fleta. Have a look at the construction process for his internal front neck block for a classical guitar. He is the only noted maker from spain who used a dovetail joint. There are others too. I test my blocks by weighing them on a HF gram scale, measuring and check for movement. What I/m trying to say is that whatever wood you choose to go with on a neck block . You want to reduce shrinkage or movement as much as possible. even for a bolt on
