IIRC, an SKS barrel is about 20". If shortening it by 1 3/8" is what you want to do, go for it. Remeber that the ones in the US can have 16+ inch barrels, 2 1/2" shorter than here.
If the new crown is better than the original, the accuracy just might be improved. Otherwise, there shouldn't be any change, unless the new crown is bxggered up, then accuracy might suffer.
The bore is chromed, so be careful when cutting and crowning.
The muzzle could be threaded to put an AR "tip" on it. Maybe even a brake or flashider. Of course, the carbine won't be any shorter with an extension on the barrel.
Cutting, threading and crowning would be a bit of a p.i.t.a. to do, given that the barrel is not readily removable. The work would have to be done on the barrelled receiver.
I'd be surprised if a shop like Epps charged less than a couple of hundred dollars to do the job, given the time that would be spent on fiddling around. Even if they treated you like an idiot, your money is as good as anyone else's.