Sorry to hear of your health issues Mike but happy to see you back!
Yours is indeed an early 110, like mine, also a 4-digit SN. The pre-66 models still use a barrel nut and headspace the same as later models but the unique bolt design required the chamber be machined to match.
EABCO used to sell barrels for pre-66 110s, I don't know if they still do.
Best wishes going forward.
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