No matter what metal I install, first thing I do is take a metal file to it. I want Clean Sharp edges & usually want them beveled In just a tad. On rounded edges same way, sharp on outside & slight bevel in. Same on a lockplate when inletting a lock.
Yep, that jewelers rouge & a honing block is a must. I think mine came from WoodCrafts, it has the V's & rounded parts. I just made a flat one & used for years, but it was a issue on the inside of the rounded ones & V's. So this lil block from there I bought ? 20 yrs ago did the trick.
That buttplate fit is definitely a GO. looks good. Put that baby on & proceed. Get the rifle all done take a lil Kiwi Dark Brown Paste wax & push a lil in the corner tip & forget it. Same way on any other inlets. Have a very tiny imperfection, seal it up with some Kiwi dark brown paste wax.