Found a Ruger Old Army with a brass frame at a small local gun show this weekend. An elderly gentleman had it on his table along with a Super Blackhawk. He said he bought both in the mid70's. Fired the OA a few times, then cleaned it and put it away. Serial number is 140-17xxx which puts it in 1974. Asked him to remove the grip panels and the frame is marked MR3DB. What is the approximate value? Thanks.