Uncles got a gun

My uncle's got a mini 30 he's had for a long time. He was going to sell it to me for cheap but it has a threaded barrel. Is it supposed to be pinned? He never registered it because he didn't think it had to be. Can it be any muzzle device if it's pinned or would flash hiders still be a no go. I'd like to get this taken care of before a transfer. Any body have a recommendation where to get this done if it needs it?