I think the lowest for a 527 are the Hunker mounts from James Calhoon, they are low enough that you may need a modified bolt handle to clear the ocular (depends on when your 527 was made):

http://www.jamescalhoon.com/

Another option is to put a Pic rail on it with low Weaver rings.

At Mackay_Sagebrush's suggestion, I put some medium rings for Tikka's on mine, found them on ebay for about $20:

[Linked Image]



Sorry, can't help with the 550.

'Four legs good, two legs baaaad."
----------------------------------------------
"Jimmy, some of it's magic,
Some of it's tragic,
But I had a good life all the way."
(Jimmy Buffett)

SotG