I do not know about your gunsmith, first I would check head space before removing the old barrel, then I would check case protrusion and compare the protrusion on the replacement barrel, then screw the barrel into the receiver with the bolt installed, if the barrel face hit the extractor I would measure the gap between the shoulder at the end of the threads and the receiver face, this would tell me the the depth of the extractor groove to be cut. I do not know if the rifle is going to be kept in a military configuration, if so the sights must be aligned or indexed by cutting the barrel face and shoulder at the end of the threads, make sure the face of the barrel contacts the 'C' ring before the shoulder at the end of the threads contact the face of the receiver, I have one M48 barrel that has a recess cut for the 'C' ring and an extractor cut.
torque the barrel without the bpolt installed, mark the position of the barrel/receiver, mark the barrel for the extractor groove, remove, cut the groove then install and align the index.
Lee's gun parts in Irving, TX. has a pile of receivers and barrels for the M48, open Tu.,Wd., and Th..
F. Guffey