I have an original wood grain dash in my 68. Its in really good condition and I want to protect. I was thinking of covering with clear vinal or black vinyl to keep it from fading and keep a somewhat stock look.
My question is will the vinyl covering adhesive mess up the original wood grain?

Don't do it. It'll change the look/color anyway. It's an old car. Live with it and be happy till it starts to peel.