I was in your same shoes. My grandfather's 721 had the first few inches of the throat burned. After cleaning thoroughly that area was dark, where the rest of the barrel was bright and the rifling still looked good.
I considered a 700 take off barrel, but wanted to keep the original barrel so ended up going with a re-bore.
I went 9.3x62, but if I were to do it again I'd go 338-06.
