X39 has a recoil of 7 pounds, so not hard on the scope itself. The biggest challenge for a scope on an SKS is mounting to keep zero. Unless you permanently alter the rifle for scope mounts it won't be that great. Receiver mounted configuration is not that great in my books. Some scout mounts over the front sight are not too bad but I would avoid rec mounted optics.
The Magwedge Kwikrail doesn't require permanent modification and keeps zero.