Remove the grips first. Those you can hand clean. Id drop in a pan of Kroil for a little bit (Hours or days) and then use a nylon brush. Then I would disassemble and clean each part with Dawn dish soap to dislodge anything that came off, also removing the kroil. Then I would drop all of the parts into an ultrasonic cleaner with Simple Green Extreme aircraft cleaner because it will not harm whatever finish is left.
The collector value will be in how much of that original finish remains.