Berthier sling and sight picture
The sling is indeed a French Berthier sling. Whether the length is suitable - you can only try it out!
As to the vision thing - you need shooting glasses!. Not glasses for driving (they are adjusted for too distant objects) or reading (adjusted too close) but for seeing the foresight clearly (about 1 yard distance). You will never see backsight AND foresight AND target clearly, so don't try to square the optical circle. Get shooting glasses AND use an add-on (to the glasses, not the rifle!) variable iris aperture which will go down to about 1mm.
That means spending some money. You will save it over the next season in the ammo that you will no longer be wasting!