How do you un-crimp and re-crimp the original steel part of the lines ?
You cut it off... Then you silver solder on a new fitting which you crimp the new hose into.... There are a few tricks along the way, first getting a crimping tool that makes crimps similar to what Chrysler used in 1970... Second since all new hose has a vapor barrier to work with R134 the hose OD while similar is slightly larger than the original.... If your truly looking for OE you won't like it, most will never know or care....
Personally I wouldn't powder coat the lines, I've always had them plated in clear zinc.... It gives the OE silvery finish where you need it & the on the engine end you paint the parts black like OE.... When you have the lines plated it's done after crimping & the inside gets plated too assuring the inside is as clean as the outside.....