The first thing I would change is the stock. I had the same gun with a walnut stock and it would shift POI a lot when it got cold. This gun cost me a few coyotes and a big 4 point buck because it wouldn't shoot straight when it got cold. Go with a decent synthetic or laminated wood stock. Free float the barrel, bed the action and chamber area.
Probably want to put a good trigger on there too.
For a barrel, considering this is a 700 yard gun, I would get a #4 or #5 contour in 22-24" length. I like Pac-Nor because its easy to send them my action and they do everything for a reasonable price. If you have a good gunsmith close by then you have many options...see which brand he likes working with. A 10 twist is adequate for most bullets up to 150 grains but I agree with FEENIX that a little faster twist would be better for a long range gun.
.270 is a great caliber for the distances you are talking about.