Barrels, You can buy a Shilen sel match grade crabon wrapped of Chistensen arms. I had one put on my weatherby and it came back shooting 1/2'' and less out of the box with factory ammo. I would also get thier Titanuim Muzzle brake that is removal with a cap, at time if you choose not to shoot with the brake on.
Actions.; if I had to look into actions I would look at McMillian or Jim bordens. I like short bolt throws so have a weatherby Mark V, but you'll have to go with a timney trigger.
Scopes. When I was scope shopping I was looking at all the scopes till I learned that second focal plane scopes you really have to shoot them at pre sighted in magnifications because Your image does not equally change in size with your crosshairs and will not have the same accuracy at ALL magnifications. I dont konw how off it could be, but I cant see spending a G plus on a Variable scope that really is variable. So I went with Schmidt&Bender Mil LP GEN II 3X12X50
Scope ring and Bases. I would look at Near Mfg.
This was my idea here.