There's a thread or two here on the forum about figuring out if your sear cage has movement and then taking care of that. Couple different methods posted in the threads (pictures, too) and it looks like either works.
When you install the race hammer you'll see it has a shallower notch for the sear (so it takes less sear movement to release the hammer).
Since the sear doesn't move into the shallow notch as deeply as it would into the deeper notch of the factory hammer the front arm on the sear doesn't raise up as high. That means the cam on the left side safety lever may not have the clearance to move under the arm on th sear. If it can't move under the sear arm the safety won't work as intended - to block sear movement and keep the pistol from firing when the trigger is pulled.
My first one I modified the cam on the safety shaft. Took me about 24 or 25 repeats of remove the safety, take a small amount of metal off the cam, reinstall the safety and try it, repeat, repeat, repeat, like I said, about 24 or 25 times. Finally got it right. Promised myself that the next time I'd spend the extra money on CGW's adjustable sear and then bought two of those for two different pistols. Worked like a charm both times.
Picture of my CZ75 Compact project pistol (converted to CZ85 configuration). You can see the arm on the sear and the cam on the safety. Flipping the safety to the safe position rotate the cam clockwise under the sear arm (to block sear movement).
Green arrow points at the arm of the sear. Red arrow points at the cam on the safety shaft that move under the sear arm to block movement. If you take too much off the cam it might allow enough sear movement for the pistol to fire, or it might not. I wasn't sure (not a gunsmith) and didn't want to ruin my safety/buy another one.