Re: CZ 527 Base
I got the DIP 20MOA one-piece one. Note that Nightforce rings will not fit on them (crossbolt rail does not open wide enough). They are not exactly to picatinny spec (as Jason @ EuroOptic and I found out recently), but it is the only one with 20MOA. Badger rings fit over top, but do not sit flush (sits on the crossbolt, but does look sturdy enough to have no problems, especially with the 527 calibers). They make just work fine with cheaper weaver rings though (I didn't try yet).
I eventually got the CZ-USA one off their website, even though it does not have 20MOA cant. With 100MOA in my scope, I should probably be ok with 223 to 600 yards.