I have one I built on a model 70 super grade 300 rum. Only a hunting rifle so I am a bit limited with the 3.6 box. With a 25 inch lilja I am getting 2900 with R26 and a 300gr. Shoots well. In the Remington it should be better yet as you can put in a wyatt,s box and stretch it out. Your old 7 mag action will work fine. Just be sure to order the rum box and your standard bottom metal will work fine. A brake would be a good idea. I have a lot of heavy rifles so recoil doesn,t bother me and I would rather get kicked than blasted. In this rifle you may want to glass the box in solid to help out the stock. If you go with the long barrel 3100 with a 300 would not surprise me. Not for the weak of heart
To add. Betram is making brass for it now and I like it.