It was built as a 7.92, then converted to 7.62 Nato when Israel standardized on the FN FAL rifle. They were probably refurb'd when the barrel/caliber was changed. Most military rifles are set to shoot a bit high at 100 yards, nothing odd there. The ammo you're using might also account for some of the POI you are experiencing. Any Mauser sight blades should fit, changing to a taller one is a common fix. What it's worth to another collector/shooter is a tough call. The recent influx of these rifles, even though the condition is different, has reduced a large part of the market since lots uf guys just want a representative example.