Just center your test model on each placing square and delete the layout helper.
Added a second version that helps to lift all models in one go.
I've also included the “M3 8x layout.scad” OpenScad file for tuning for another printers, just change the first two lines to whatever dimensions your printer has, press F6 (render) and then F7 (export to STL).
The “M3 8x layout v2.scad” OpenScad file can also be easily changed.
The author hasn't provided the model origin yet.