First welcome.
I can't help you on your slide focus scope. I have mounted scopes on my SKS's. The key is going to be they Mount. Those top cover mounts just don't work well. That leaves you with a drill and tap option, or Murry's idea of threading the take down lever hold. I haven't done that yet, so I will leave that to others.
IMO scopes main purpose is to put the eye/sight/target on a single focal plane. a 2x and 22x will both do that. I grew up hunting in the thick woods of La. There unless you were on a "pipe" line, shots were under 50 yards. At 4x I've thrown up my rifle and seen only hair a lot. So I gravitated to lower power scopes. Most of mine are 1.5 to 5 or 6, or 2x7.
But hey, your gun your money do what you want. I just don't see having a mega powerful scope for a cartridge designed for 300 meters.