Cutting the stock ... straight and square to the old cut , is the hardest part . I did mine but I had access to a Table Saw and a friend who matched the new cut to the old cut , shortening the stock 3/4" for my young daughter.
That was the hard part ... the thin rubber recoil pad I simply sanded down with an electric belt sander clamped up right in bench vise ... I taped the finished stock and sanded slow and careful untill I got to the first layer of masking tape .
It is best to sand it down to the wood so it's all flush , level and smooth but then you have to refinish the stock !
It's not hard if you have a few tools and can get that stock cut right .
Gary