Re: 50 MOA adjustable scope mount
I'd agree w/ mesh... Get some 'regular' LR bases... Leupold makes a 15MOA 1-piece Redfield style dovetail base, Badger Ordnance makes a honkin' big 1-piece 20 MOA picatinny/weaver rail, and Ken Farrell makes some pretty nice 20MOA (think he also makes up to 30-35) two-piece weaver bases. Combine those w/ the Burris Signature 'Zee' rings (Weaver base) and you can get a butt-load of elevation available for a reasonable amount of $$$.
My only gripe about the Burris rings is that along side something like a set of GG&G or Badger Ord 30mm rings, they seem kind of... wussy. But, if you need the elevation shims, it's about the only game in town other than a custom setup.
Just out of curiousity, what do you need that much more elevation than what is in your scope already? Even a .308 Win "only" needs about 35-40MOA to reach 1k. What are you using, and how far are you shooting?