Interesting that the rib survived a hot bluing as it was soldered on and not an integral part of the barrel as in the solid ribbed M17 Rem. Serial numbers pre-855,000 barrels aren't randomly interchangeable, but Les Hovencamp can fit a pre-855,000 barrel to any M37 and it doesn't require the intricate process that the current Ithaca shop undertakes. He fit a 1940 barrel to my 1957 M37 20 gauge and opened it from full to IC to complement the existing M. Les was the head of gunsmithing at Ithaca many moons ago.
Barrels for sale:

http://www.ebay.com/sch/i.html?_from=R40...el&_sacat=0
Back to the rib on the 37R. At what temp is solder applied versus hot blue temps.? Is there a danger to the rib if hotblued or is it an oft repeated urban legend? Gil