Flat back to replace the back with a lug that ships with the cheapest metric dial indicators money can buy on eBay (~$9 delivered!).
Details: I really wanted to use kyoday's awesome Gauge Dial Calibration for creality Ender 3 MOD, but the rear lug on my dial indicator got in the way, so quickly threw together this flat back.
The provided settings are just what I ran and worked great in PLA, printed with the counter-bores face down. I didn't bother with supports for the counter-bores, figuring it's easy enough to spin a small drill bit or chisel out any offending overhangs if needed. You can probably go lower on the infill since it's not structural.
You can easily kill the counter-bores altogether in the code, but you may not be able to use the screws the indicator came with.
Inside the dial indicator there's a retaining screw for the main spring around the outer perimeter, it was loose so I tightened it down slightly so the back could be mostly flush. Your mileage may vary and you can of course make a divot for it in the scad file if you so choose, but I decided to keep it simple and so it can be screwed on in any orientation.
The eBay listing from the seller I used seems to not be up anymore. But I believe the search string "0.01mm Accuracy Measurement Instrument Gauge Precision Tool Dial Indicator" should get you a lot of listings.
Here's a link to one that at least looks identical to the one I bought: