Based off the pics I am starting to agree with Billpa and think that this is more of a bad milling job rather than a twist, or at least a combo of both. The action screw hole look to be correct or at least a lot closer than the rear bridge is.

It looks like your 1pc base is sitting darn close to parallel with the long axis of the rifle. If the action screw holes are indeed straight then I would say either milling the rear bridge flat and then putting shims (or bedding) the rear of the base would be your best option, or bedding as is and watching it like a hawk for awhile. Either way I would plan on using Burris Sig Zee rings so you can get your scope aligned properly for sure.