Matt, H&R will fit 357 and 44 mag barrels to any SB1 frame made 1987 and later, if your frame was made since 1987, you should be fine, if it was made before 1987, it may still work fine since the original H&R offered the 357 on some of their old cast iron frames, the part of the FAQs Stimpy quoted was written before H&R started offering SB1 357 and 44 mags and still applies to other rifle chamberings.
Tim