the difference between the carbine and rifle were stock design and length of barrel. The carbine looks more like an M-1 Carbine with curved butt plate , front barrel band and 18.5 inch barrel . The rifle had a longer barrel, at one time 20 inch ( I think ) , no front barrel band and a flat butt plate...looks more like a conventional sporting rifle.
Ruger no longer shows the rifle in it's line up. They put the sporter stock on the 18.5 inch barreled action and call it the "Sporter" model. If the rifle has a longer barrel you may want to hang on to it...collector's like stuff no longer cataloged.