I would assume that the original finish was bluing, not park. I used to do a ton of rebluing when I worked for pistolsmith James W. Hoag, back in the day when his guns dominated the Southwest Pistol League, the Bianchi Cup and other IPSC competition. Jim might still do jobs like that, but I would expect that the customer would need to give it some time. Jim's still a busy guy and works alone now.
That plating would have to be stripped and the gun polished before bluing. That's going to take a bit of $ and time. But if interested, let me know and I'll get you contact info. Jim's bluing is a very dark color, almost black, depending on the steel alloy. One could also go with a bead blasted satin, or sand blasted matte finish, which would save some of the polishing costs.