Wanting to build a ultra mag repeater but have questions

As the title states I wanna build a ultramag repeater, my question is: If I all I have is a long action, where or how can I go about opening up the action to accept the ultramag rounds? I will also need bolt head and magazine assembly, but where would I find them?

You should just need a standard magnum boltface, so it your donor gun is a 7mm Rem Mag or a 300WM you are good to go. If not then Midway or Brownell's will have the proper head for you. I believe they both have the mag-boxes too.