Bearhunter & millwright are correct. Seems this M1 carbine barrel add-on issue has to continually be addressed. Semi-auto, centre-fire, fully rifled (except chamber) for greater than 470 mm (18.50") is the law now. Most common N/R length is 485 mm (19.1"), and 476.25 mm (18.75) . Externally, the extension seam is usually hiding under the front sight, so you can't see it til you look into the muzzle. Might be a smooth sleeve, or piece of 9 mm barrel.
I recently worked on a Gen III Universal, wasn't cycling properly. This is the first one I have had in my hands, and I have to say I was impressed with the quality of workmanship. New design features were intended to improve the USGI design, ie dual return springs, bolt hold-back feature, receiver drilled & 8-40 tapped for a side mount scope, but the major problem of cracking return slide is the flaw. New replacement slides are avail in US at around $99 USD. They are heat treated (as were the originals), so repair welding of the crack(s) is not a good idea. Gen III's also have an interesting feature of the gas port having a 2 position setting, one for S/A, and the other is for single shot.
The Gen III barrel/receiver are NOT compatible/interchangeable with USGI parts, so Criterion N/R barrels don't fit at all. Gen III's are a lot more difficult to rebarrel.
You can apply to register this carbine, as long as you have an RPAL. RCMP Firearms Registry is generally sympathetic to the M1 carbines with extensions.
Asking price of $400 -$450 with mag is about market value.