I am in this exact same position. I got a long action for a 6.5x284 build and it came with the double stack magazine. It used to be a 7mm Mag. What a battle just to get the old mag well off the action ??? I have absolutely no idea how they fitted it in the first place ?? Some Ideas that Savage has fielded over the years are just as dubious as hell.

I also note like mentioned by others, that stock of Savage parts seems to have dried up some time in mid 2013 and has just not come back. I did get a bottom metal and DBM for a different long action build that was on an original centerfeed action and that just bolted right up. But I have not found more hardware since about June 13.

Worst come to worst, I will do another single shot adaption using a piece of aluminum sheet and just wait (if ever) for the stock of parts to come back, something similar to rimfire ammo...