Regulator is an easy install. Depressurize it, remove the end fill cap of the tank, press the regulator into the tube till it bottoms out, make sure it is adjusted to desired pressure, and replace it with the new end cap fill gauge.
Then pressurize the tank.
When installing a regulator you have to get the end cap with the pressure gauge on it along with the regulator. If not you do not know what you have the tank filled to. The existing gauge on the rifle will only show the regulated pressure after the regulator install.
Re scope, I have Bushnell Elite 3200 5-15x on it. Wish they were still made. I would have a few more of them.