I just purchased the 527 .223 Varmint walnut stock. There are no iron sights only dovetails for mounts which are 16mm. The factory scope rings you can purchase for this are medium (which turns out to be everyone else's high), and happens to be the highest ones you can get from CZ. I must say they are top notch steel rings, well worth the 55 USD charged. BUT they will not allow you to mount most (all?) 50 mm lens scopes as the scope won't clear the barrel. I don't see any other problems.
Needless to say I looked all over for ones to mount the scope that came off my AR-15 a Bushnell Banner 6x18 - 50mm scope but ended up with a Simmons, same thing but only 40mm. I love the rifle, I thought it would be to heavy because of the larger diameter barrel but it is very well balanced to carry around. Much lighter than my Bushmaster, (new scope is lighter also).
I am surprised at the number of readers on here, but no one seems to answer posts?? For such a great rifle to have so little interest generated is a shame. Hope this helps... I will try to help whenever I can.