Ok, I'm going to resurrect a project from the past, building steel bodied guitars, that my son and I were going to go into, but he ended up pulling out, so body of the guitar will be cut from 1.2 mm mild steel, but I need to fit a wood block inside to mount the neck pick ups are hardware to, therefore gluing the steel to the wood
If it's just the pickups even old chewing gum would probably do it!
But joking apart, I think some protyping will be needed. If you have an entirely ridgid bond, that will probably result in a different tone than a slightly dampened bond. Noone here, I suspect, will be able to tell you which is better to the ear?
i would imagine (having no knowledge of instrument making) that sikaflex or the like would be likely to have damping effect. id use a rigid adhesive like a decent epoxy
Can you put a nut sert or riv nut into the steel and mount the pick ups into that or.
Or another option would be to use the threaded inserts into the back edge of the wood and long screws through the lot to pin it.
If after an amazing product for bonding I use 3m panel bond. Used for sticking most stuff to most stuff but now some gorilla glues are impressive also.
There shouldn't be any damping effect whatever you use as long as the bridge is solid mounted and if it's using electric pickups that would also cancel any damping.