Thanks for all of your inputs. There was a video in Issue 5 of
The Sporting Shot on-line magazine about both hot bluing and rust bluing processes used in the restoration of a Wnchester model 21 (
http://sportingshot.imirus.com/Mpowered/book/vsport10/i5/p1 ) The article containing the video starts on page 98. From your comments, it appears that the issue with hot bluing of soldered barrels is the potential for latent corrosion and possible delamination of the rib and barrrels if residual bluing salts are not properly rinsed out.
The video does suggest that one can obtain the same deep blue finish as hot bluing with a sufficiant number of passes. (In the case of the Model 21, 15 passes were done to "match" the hot blued frame.
By the way, the article about my unusual Marlin Model 90 Skeetking starts on page 68 in the same issue 5 of
The Sporting Shot.