You will need a chop saw with a fine tooth blade and some sort of jig to make a square cut. Then you will have to refit the pad or install a new one, requiring a pad jig and a 10" disk sander or really big belt sander. Unless you have done this before, I would not run the risk of screwing this part up and would leave this to a gunsmith. The refinishing part is not all that tough and there are volumes of information about that. Depending on how much you need to shorten the LOP, you might be able to accomplish this with a thinner pad rather than cutting the stock.