If I understood it correct, Walt was essentially discussing the problem of installing a previously installed barrel with respect to clocking and headspace/chamber length. Same issue we've encountered with milled AKs, and Galils, just to name two, when using previously installed screwed in barrel. Peening and/or shims can get you to proper clocking, but still have to contend with headspace and supported chamber length.
The chamber length will still be the same relative to the barrel. The assembly of peened/shimmed barrel and receiver will effectively increase the chamber length with respect to the receiver locking lugs.
If needing to adjust clocking, I'd think shims would be a better route vs peening in that with shims I'd think you'd have a larger mating surface than that of the peaks and valleys created with peening. With a very small gap adjustment, probably doesn't matter though.
How does your M-14 clone headspace? If your M-14 barreled receiver does not have sufficient headspace to close on proper 'go' gauge with barrel clocked correctly after shimming and/or peening, then you should be able to ream the chamber to set minimum headspace - assuming the bolt is not contacting the breech end on the barrel when bolt is in battery while using head space gauges - and be good to go.