Too bad about the bore condition but it sounds like it is not bad overall. Keep trying to clean it as best you can, and adjust the bullet diameter as best you can and it may shoot well.
As far as the sling, here are the three primary slings used by the Italians:
The top is of course the Italian-made "98k" style sling - from earlier posts you are familiar with this one - designed for an Italian sub-machinegun but found occasionally of short rifles.
The second is the earliest sling used on the M1891 long rifle and the short rifles with wide swivels. This sling was originally in use on the Italian Vetterli as well as the earlier Italian Albini and saw use on the long '91 from it's acceptance in service until the end of WW2. It has no buckle, it's adjustment is done with studs at either end.
At the bottom is the most often seen Italian sling and it could be and was used on all Italian rifles, before, during and after the 2nd World War. It has a tongued brass buckle.
All three of the above slings are original, none are reproductions.