I don't know if you want to keep it original and not remove the curve or not.
If it was me, I would plain it off straight to proper length of pull for the pad your using.
I like to use a bench planer or a hand held power planer clamped in a vise. That has worked better for me than a radial saw or a table saw for a clean, (no gap), flat surface to attach a pad to. I also recomend a recoil pad jig from Brownell's. It has worked great on the 6 or 8 jobs I have done. If you do two recoil pads, it has paid for itself over having a smith do it.
I have seen pads installed on the factory curved butt. I thought they must have warmed up the pad's base spacer to get it to conform to the curve. But I really don't know. If the curve is shallow, the pad may just conform to the curve by the tightening of the screws.