[Shortening M1 Length of pull]

Just got an M1 Super 90 with the pistol grip stock. I want to shorten the LOP but I would prefer to do so without cutting on the stock. Does anyone make a replacement butt pad that is thinner than the stock one?

Thanks!

[Super 90 vs. M1 Super 90]

Are all Super 90s M1s? Or, are there earlier Super 90s that are not M1s? If so, what are the differences? A buddy has an older Super 90 that does not say M1 anywhere.