Quote Originally Posted by darkker View Post
Remington has a long action, and a Magnum action; different birds.
This isn't correct. All Remington 700 long actions are the same length. Standard and Magnum actions are exactly the same. The only difference is the feed rails are slightly opened for the RUM's.

Back to the OP....The cheapest and easiest would be to find a used center feed long action magnum.

Probably find an old package 7mm for $200-$300.
Swap on your barrel.
Get a Boyd Pro Varmint that is inletted for factory centerfeed bottom metal. Bed and pillar it. $129 plus shipping/options.
Install Accurate Mag bottom metal. Uses CIP (3.850") length magazines. $185.

You could also go with a chassis system, but they are expensive and tough to find one for longer or CIP length magazines.