As with the original butt plate, the recoil pad will have to be fitted to your gun. The best thing to do is give it to a competent gunsmith to fit one.
Also to remember that if the length of pull was good for you with the butt plate, unless you get a thin recoil pad, your length of pull with now increase about an inch more.
In my humble opinion, there is no need for a recoil pad especially during the hunting season when you will most likely be wearing heavier clothing.
If the recoil bothers you, most likely you are using too heavy a load.