[Bluesman]

Ron Butler stamped the year, the month and the chassis numerical sequence up on the main rail/driver's side frame between the front suspension and the radiator. I don't know anything about the Arntz chassis but if it is a Butler this information will help dating the car and perhaps it's owner history.
$20,000 sounds very good. I don't need to tell you tho... check it's title and how feasable it will be to register and insure it for the road.