For anyone looking to swap out round trigger guards for squared ones, it's not as simple as it seems. The older guns with the rounded guard used a crescent shaped slide stop spring that is retained in position by a recess milled into the side of the trigger guard where it latches onto the roll pin in the frame.
When they switched over to the squared trigger guard, they also changed the slide stop spring to a L-shaped design that it no longer held in position by the trigger guard recess (it's retained by a hole drilled in the frame). The squared trigger guards thus, lack the recess for the slide stop spring that the round guards have.
So to use a squared trigger guard in an older gun that uses the crescent-shaped slide stop spring, you are either going to have to modify the squared trigger guard to be compatible with the old style springs, or you'll have to have the frame drilled so it can use the "L" shaped spring.
You can change the trigger guard to the old style on a newer CZ 83 without issue, but not the other way around.