If you want to hit 3000 with a 180 you will need a 24 to 26" barrel if you you go with a 7 Dakota
or similar. The other option is to go with a 7 RUM or 7/338 Norma. They will push a 180 at 3200 with a 26" barrel. By dropping to 22 to 23" you might reach the 3000fps limit. Figure on 35 -50 fps loss per inch.
Twist will probably be 1 in 9"
I am in the process of a similar build. I want a light weight pack rifle that will reach 600 odd yards, only deer size as no Elk in NZ. I have gone down the Remington Model 7 7SAUM path. I should get 2900 -3000 but with a 162 a-max.
I have fluted the barrel, threaded for a radial muzzle brake
, fluted the bolt and replaced the firing pin with a lightweight one. I have built a carbon fibre stock for it. I will use a Bushnell 6500 2.5 - 16 x42 scope in Talley light weight rings. The rifle should end up in the 6.5 -7 lb range.