Dear Sir:
About 3 years ago, I sent a .357 Blackhawk back to Ruger to be fitted with a 9mm cylinder. Ruger did the work and returned the weapon promptly, charging about $65 or $75, if I remember correctly. Unfortunately, within the last year, I have been asked by several customers to do the same but in each case received another response from Ruger. The first time, I just shipped off the weapon with the request to do the work. It was returned in about 2 weeks with a note that Ruger did not do that type of work any longer. Since then I have called for two other customers and each time been told the same thing--Ruger no longer does that type of work and I should sell the customer a Ruger combo.
I think there is room to hope, however. Ruger is generally a pretty good company about customer service. Even though I've been shot down three times, I get the sense that if you're really persistent and get to talk to one of the gunsmiths on the phone, he will probably tell you to send it in. My sense is that the folks that answer the phone and open the boxes have a set to rules and regulations, but if you can get past them, you have a good chance. Best of luck. Steve