The import stamp will be on the barrel, toward the muzzle, typically on the underside. Will be a name and short address. Blue Sky Imports out of Arlinton (?), VA being the most common.
Lack of stock cartouche not unusual. Any there should be on the wrist of the stock, normally on the left side. A "P" may be stamped on the heel of the pistol grip. Rebuild stamps are normally a two or three letter code, they can be quite small. Ordnance wheel cartouche is usually quite large and prominent, and generally not seen on rebuilds.
Don't get hung up on the term "original" carbine. Virtually all of them went thru rebuild at least once and many several times. The adjustable sight and bayo lug definitely mark this one as rebuilt. Serial number and barrel date are a pretty good match, probably the original barrel.
Even for an import, if the condition is as you say, this is a pretty good price. Carbine price tags these days are just nutty.