I have a couple of older Cateye wireless bike computers that didn't come with stem mounts. I saw a couple of models on this site that were close but wouldn't fit. mread's frame mount for the Strada seem the closest. The Strada's mount (and most newer Cateye wireless computers) is different than my Micro Wireless and Cordless 2 (CC-MC100W and CC-CL200) and therefore doesn't fit them. So I started with that one and combined some of the features of hobbyman's harness to better fit and add the unlock lever goodness.

Note that for the stem mount your bar stem needs to be pretty long to allow room to slide the computer down onto the mount. Use 6 in. zip ties to affix the mount to your stem as the 8 in. ties are too wide.

For the headset mount first make sure that you've already tightened your stem bolts to the steerer tube so that you don't have to use the headset cap for compression anymore. you'll need to have enough room on the steerer tube above the stem to fit part of the mount's spacer. You may have to do some spacer gymnastics on your steerer to achieve this. While you're doing that make sure you don't leave any exposed steerer tube above the mount's spacer or you won't be able to tighten the headset cap onto the spacer to hold it tight.

As for printing, I had the best results printing the object at a 45 degree angle with 5-10% support (as columns) and an overhang angle of 80+ degrees and a brim to minimize support cleanup.