Firing pin block was added
Front sight is now removable
Safety internals were improved
The frames magwell was changed
Disconnector was changed.
Drop free mag break.
Trigger guard
The hammer changed, both in shape and width. (Because of that change, the Kadet Kit won't work on many of the older pre-Bs: because the hammer is too wide to fit into the slot on the back of the kit, and can't reach the firing pin.
The firing pin stop (a plate) was replaced by the firing pin retention roll pin, which has had several versions.
Expanding on the point, above, the safety mechanism changed from the earliest models. (The oldest ones had a pin hole through which you had to insert a pin or nail to capture the internal spring -- if you didn't, it could go walkabout upon disassembly, and there are no replacements easily found.)
Grips changed in appearance. (If you've got old-style grips in good shape, they have a pretty good resale value -- which would allow you buy some nice wood ones. I've gotten $45 for some older ones. (They all fit the same regardless of model.) I prefer the factory soft-rubber grips.
The shape of the slide release changed - pre-B and B slide releases look different, but should work the same..
Some of the other pins are now different in the newer models.
The rear sight has a different dovetail than the newer guns.
The old front sight
is removable -- but not easily. It was STAKED (the underside of the stake was expanded on the inside of the slide.) Trying to find sights for a pre-B can be a challenge, if you want to do it yourself.
If you want mags to drop free, you can get the flat (straight) CZ-85 Combat mag brake, or simply straighten the one in the gun....
If you haven't done so, you should visit the CZ Forum
http://www.czfirearms.us/ People there have forgotten more than I ever learned and still know a lot more than I do...