I tried everything, finally fitting a solid SVD sidemount to hold a 4X Romanian POS drilled and trapped onto my beater Yugo SKS (never would drill the collectible Tula, of course.) It looks cool and gets about as good performance out of an SKS as any scope and mount can ever give.
The single-piece scope mounts integral to a replacement rear cover are better than the others (about $25 on fleaBay), but still sloppy - the trick is to carefully line the thin upper edges of the receiver/cover joint with a small amount of JB Weld epoxy to bed the cover in, stopping some rattling around. This at least keeps the cover/scope from rattling around, but it still is a lousy setup. You can mount a short fixed 4X armored scope in one and be able to see well enough, but it ain't a Remington 700 so don't expect much!
The truth is that only a drilled, tapped, fixed mount works well on any rifle and you sure don't want to damage a collectible rifle. Honestly, an SKS is so intrinsically inaccurate (perhaps 3-5 MOA) that a scope is not really a big help. These are just not long range rifles and 300 yards is all you'll get even modest accuracy out of one, particularly with el cheapo milsurp ammo.
This loose accuracy just comes with the rifles and ammo - with top handloads I can get down to a consistent 3 MOA 5 shot group with the scope at 100 yards, but even that fades as the rifle heats up.
My Saiga AK was factory tested to about 4 MOA at 100 meters and the target came with it, a bit worse than the SKS but a realistic bench test of what can be expected - these were never tack drivers but were built for reliability - it is said that even a blacksmith can fix an SKS!