It depends if it is oil finish or laquered type finish.

If oil finish you should be able to redo it
but you may have to take it back a small amount
so it desn't become patchy.

How do you know it's the original finish ?
Alot of English guns were refurbished every year or so
and alot of guns people think are original, aren't.

Re the "small holes" - they could be borer holes
which means you should check the stock to make sure
it is sound inside and not hollowed out by the
pesky critters.

May need to be careful the buttplate doesn't fall apart
if you take it off - they tend to be delicate / brittle.

No idea how to restoring - you can get new ones
made from horn.

500 Nitro