This directory contains designs for testing drill press runout with a dial indicator. They currently fit a dial indicator with an 8mm stem.
You can find video of it in action and more information at PCBurn: https://pcburn.com/measuring-runout-on-a-drill-press-(3d-printed-tool)/
Drill_Runout_Gauge_Holder-Mk3: Standard gauge holder. Use a 3/8 screw and fender washer to hold it down.. Has a slot for a 14mm groove oriented toward the drill chuck Drill_Runout_Gauge_Holder-Mk3-No_Groove: Same, only with no slot to fit a 14mm groove oriented toward the chuck on the drill bed Drill_Runout_Gauge_Holder-Mk3-Super_Stubby: Stubby version. This has a 14mm slot but is much shorter and as close as I could get it to center. This'll work with very short stems on a dial gauge.