I also have a No. 1 and 3 and both have custom barrels on them. No. 1 is set up with 348Win. and 22-250 barrel and the No. 3 has one in 6BR and 45/70. All barrels are from Douglas Barrel Co. and upon starting this venture, was warned that the dimensions of the two receivers needed to be taken into account in order to set the head space. Go to Ruger web site and review the takedown video on these rifles for it is a great help in taking them apart which you will have to do to change out the extractor.
Once it is done, no more mysteries in doing so. Both rifles give very good performance regardless of which barrel/caliber it is set up with, great rifles.