He'll need scope rings as well. Make sure and check the width between the dovetail grooves on the gun. Older guns measure 13mm, newer guns measure 11mm. Get him the correct size rings.
Sportsmatch makes a 13mm ring set. I have used a set before without any noticeable problem but another forum member said he experienced poor fit. Unfortunately I am not aware of anyone else who makes rings for 13mm dovetails but then, I haven't looked extensively. Figure out what you need and go from there.
You have been steered in the direction of small, low power scopes which is fine. If for some reason you consider higher magnification scopes with long scope tubes remember, the bell of the scope needs to clear the barrel locking lever, not just the breach when the barrel opens.
Your pops has a fine gun. Keep it and the rear diopter sight in the family!