"...not the same as re-barreling other rifles..." The only difference is how the headspacing is done. Changing bolt heads with headspace guages is how the headspace is adjusted. Same use of a barrel vise and a proper action wrench otherwise.
"...have "bad" and "awful" bores...." Please define that. Heavily pitted/rusted? The rifling is not square cut like American rifling. It's shallow. This ( as opposed to this [.
"...slug the bores..." Absolutely. Lee-Enfield barrels can measure between .311" and .315" and still be considered ok. Over .315" is shot out.
In any case, like Hal O'Peridol says, Gunparts lists 'Good to Very Good' used No. 4 Rifle barrels with the front sight base at $64.85 each. You will need a barrel vise and the right action wrench or a smithy who has 'em. You can install the barrel to use the bolt heads you have, but it must be done with proper headspace guages.
"...my favorite utility rifles..." You want to check the headspace on that one too. Thousands of both models of Lee-Enfields have been assembled out of parts bins without ensuring the headspace is ok.
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