Your rifle, at one time, was a WWII military rifle - with different wood stocks, and before that front receiver ring was drilled and tapped. Since there is no evidence of holes on the cross bridge - is likely it was once set up with a Parker Hale A20 front scope base and used a Parker Hale A21 rear base in place of that rear sight. As is, looks to me like a sporter conversion - likely terrific for deer or moose hunting, but has not much to be a "milsurp" left on it??
I am not aware of any military that stamped the word "custom" onto the barrel. That front sight ramp is not military, and I do not see bayonet lugs - so is likely an "after service" or truly "custom" barrel that was screwed onto that receiver, at some time, by someone. I am not familiar with the purpose of the hole into the stripper clip slot - above and ahead of the ejector screw - that hole was not a military thing, as far as I know.