[Quack me up!]

I have a 10ga top lever hammer gun that I am going to be adding a Silvers #3 pad to in order to gain a little LOP.
I want to retain the curve in the butt plate so I can put the steel plate back on if need be.
I am just looking for any hints or tips on fitting and grinding the pad to fit.
I have access to a heat gun and also a 12" round sander.
Is there a particular grit paper that works well for shaping the pad etc.?
Any tips would be appreciated.