Per McIntosh, p. 283: "I've been told that Savage Arms began boring new Fox guns to 2 3/4" immediately, but there is evidence to suggest that this may not be true. Quite a few work-order cards from the 1930's specify 2 3/4" chambers, but a great many do not. So I have to wonder: If the longer chambers were standard, why mention them? I have a notion that they didn't actually become factory-standard until mid-decade or thereabouts."
Researcher, McIntosh seems to agree with you on the rechambering thing. I must've been misremembering that part, or confusing it with the above. From p. 284: "Eventually, Philadelphia Foxes received at Savage for repair were rebored to 2 3/4" as a matter of course and were stamped accordingly. I don't know when this policy was inaugurated, but I suspect it wasn't until the early 1960's." He goes on to give 1965 as the year when barrel wall thickness was measured, and if the gun passed, to rebore it and proof-test it.
