They are probably made long due to variations in SKS receiver dimensions. You'll have to file down the front edge to get a snug fit.
I haven't had any long term success with any of the replacement cover style scope mounts. They either become loose causing loss of zero or you lose zero when you field strip for cleaning.
The best scope mount for the SKS is made by Choate Machine. It is a steel mount that screws to the left side of the receiver.
SKS scope mount