Need help identifying/authenticating Shelby Daytona Painting

Hello,

I'm new to the forum and hope you can help. I work at a museum that has come into the possession of a beautiful painting of a Shelby Daytona Coupe at Sebring by George Bartell. What I need to know is if the piece is the original painting or if it is just a print. I know the image appeared on the cover of Sports Car Graphic Magazine in June 1964 to celebrate the Cobra's victory at Sebring that year, but I cannot find any other reference to the image, which leads me to believe that this is an original work. Link to pictures is below. The item also has a receipt for $1,500 on it from 1985.

http://imgur.com/a/M67dh

Can anyone verify this or give me any helpful hints on how to verify this?

Thanks in advance!