I am glad to hear somebody else out there is actively restoring a GMC. Gives me hope and strength to continue on. Like you, I pay attention to detail. It's the small stuff that matters to me, and when it's all done it's all the small stuff that really stands out. Decals, white paint on your light switch letters, dash nomenclature, etc.
I don't know if anybody else has thought of it yet, but padding the dash bar on the passenger side and adding seatbelts to these trucks is an important safety feature. The GMC brakes will throw you out 50 feet onto the pavement if you stomp on them in an emergency.
I will be putting some of that foam pipe insulation on my dash handle and making a lace on vinyl cover that matches my upholstery. Keeps from denting the passengers head if they should forget to buckle up.