It’s definitely going to vary a bit depending on the geometry of your print. When tolerances are crucial, I usually just do a test print then adjust and iterate until it’s close enough. To achieve truly perfect and consistent results you’d probably need to do some subtractive machining afterward (e.g. undersize your holes then drill them out).
In any case, I would suggest measuring your block and inputting an X/Y and Z fine tuning as appropriate. Here are some blocks I’ve used for calibration in the past if you want them:
I don’t think you need super-tolerance for a Lego brick. I recall people have done them before.
If you do figure out a scaling factor etc. that works, let us know!