Are you just trying to increase LOP?
If so, you could cut a scrap piece of plywood (of desired thickness) and sand to fit as a spacer between the butt and the plate. The toe may be a little funky because of the angle but it will work and can easily be restored for re-sale. I have even done this with cut up flip-flops
Grinding to fit a recoil pad isn't particularly hard if you have the right tools but there is an art form to doing it so it looks good. I F@%Ked up the first two I tried before I got it right. I think I am pretty
good OK at it now (humble brag
)
The easiest way is to mount the pad then grind/sand to fit THEN refinish the whole buttstock. Sometimes, that is not a bad option depending on the condition of the buttstock.
ETA- Like Bud said, why not a "small" slip-on Limbsaver recoil pad. Walmart or Amazon usually have them pretty cheap. Perosnally I don't like the "look" but easy installation and easy to remove if you don't want it anymore.