I bought these guys
http://www.buymilsurp.com/magazine-base-metal-tt33-pistol-p-3350.htmland I cut up one of my original base plates. you don't need to file the front at all. you do need to file off about 1/8th of an inch off the back. and a notch in the side for the spring so that the whole thing stays together.
you have to cut off the rear 1/4 of the old base plate, and install it on the bottom of the magazine, then install the plate from the website with 1/8th inch cut off. I had to pry a bit on the magazine to get the bottom a little wider so that the new plate fit very snug, since you finger is resting on it. having slop in it was anoying.
it takes a little bit of mesuring for each part as they are not exactly the same, and you want it to sit farther forward. it was dsigned for the TT33, and it fits perfectly on there, but since the CZ has a bit of a angle there already it has to slid forward more.
if you don't want to cut up the old base plate they sell them also.
http://www.buymilsurp.com/magazine-base-cz52-cz-52-cz52-pistol-p-397.htmlyou only need one as you can cut 2 1/4 sections out of it, and with a little filing it works great.