Skip's suggestion is what I would go with. Just be careful with a heat gun as the surface of the wood can heat rapidly and burn. Another option is to heat a palette knife and work that in to the space between the end block and back. It will be difficult to match up the sides and back when you re-glue, but if you take your time and are very patient you can do it. Best wishes for the successful completion of your project.
Ken
"The dulcimer sings a sweet song."
