.222 Remington used to be an awesome benchrest cartridge. It and the rifles it was chambered in tend to be very accurate. As said, the barrels are slow-twist for lighter (shorter) bullets, so not compatible with some of the bullets that have become common for .223/5.56 in recent times.
It would probably make a lot more sense to load some great .222 Rem. cartridges and enjoy that rifle as-is than to alter it to be a .223. Lot of work and cost for no clear gain.
You might save a little (well, back in the day you could have...not these days) in using surplus 5.56mm or common .223 Rem. ammo, but it may or may not work in that barrel anyway.
A vintage .222 Rem. tackdriver is a proud addition to any rifle collection!