I think that you may want to check the crane for the model number before doing anything else. The model 29 was never a stainless gun, it was either nickle plated or blued steel. Since your reporting a rust issue, I suspect that you may have a nickle plated model 29. If that is the case, the nickle plating can be removed and the gun then blued because the nickle plated frames are simple mild steel, not stainless. All that work won't be cheap, but if your willing to spend the money, it can be done.
As for blueing a stainless steel model 629, stainless steel will turn blue when exposed to heat and oxygen, but the resulting blueing is extremely thin and will wear at the lightest touch. So, it's not a good idea. A much better choice would be to use one of the paint products that are now available and fairly durable. IMO, a better option to restore the finish on a stainless gun is simply to wet sand the effected areas with a 1200 grit sandpaper and then use the appropriate grade of scotchbrite to duplicate the factory finish marks, of just give the gun a full polish.