I had a nice limbsaver pad that would have worked on that, they are a hi end pad, but sold the last one at last gunshow
You have to grind them to fit, easy with a jig and belt sander on a stand.
But it's doable with out a jig.
All you info on the gun is on the barrel flats, chambers, chokes, etc.
And as others have said forget the 00 buck shot for now and just one finger in the trigger guard, and light lead to start.
Those old pads go like that because the gun has sat in a rack on the rubber for about 50 ys.
If you want a quick fix, check out the flipflop pads, I will not tried it ,never had flipflops, but if no one is looking?
BTW there will be 2 screw thro the rubber, usually Philips , hate them, top will be down about 3/4" in center, bottom will be about 1 1/4 up from toe/ bottom , poke around with screw driver , you should feel the holes, start with a small pointy flat one till you find the screws.
If you have a new pad, just cut the old rubber off is the easiest, then take the screws out .
If you have to make new holes , glue in wood dowel first to plug old holes.