Need fair market value 69 Chev pick up

[suemeiou]

I am thinking of donating my old 69 Chev pick up to charity before the end of the year, and I am trying to dtermine what fair market value would be. It has less than 30K original miles on it, but it's pretty rusty. It's 3 on the tree, with a non-working gas gauge. It was my grandpa's truck off the farm. The wooden floor of the box rotted, and he put steel plate over that, but it's rusting badly as well. It has been stored in a garage the past two years, but was running when I put it away. Any idea of value? Thanks.