Plywood body and maybe a bit of thin plywood cut to the size of the neck pocket as a shim would be the first thing to do and then drop the neck in over the top and re-check action height to see where things are at and which end needs how much sanded off to bring it somewhere near a decent level/angle to play.

The fresh plywood should be easy enough to sand into shape rather than trying to use a solid piece of timber such as maple or pine and would be harder/stronger/tougher than just pine on it's own.