Try just cleaning it first, you may be surprised. Gun oil and bronze wool can get a lot of surface rust off without hurting the finish too bad.

Clean it carefully with bronze wool, not steel wool! I bought my bronze wool on eBay and I'm always impressed with the results I get with it. Be careful and don't do anything that you will regret, but as this gun has sentimental value to you, I'm sure you'll be very careful!

Art, I see only three grades of bronze wool on Ebay. Is Fine (#0-00) fine enough for this work?

Tom,
Yes, I use "Fine" grade and it really does the job!!

Thanks Art,

I just got a Ruger Standard (1954) @ our gun show last weekend and there is a little rust under the grips that I need to take care of.

Tom,
I apply a little light oil and lightly rub the rust spots with the bronze wool, then apply a very light coating of Rig grease to prevent further rusting...