im not sure if what you're saying will apply to how im doing my build, since im not building it in the most ideal way.
my build has a weird evolution… where i spent a lot of time planning, and bought a bunch of stuff, had stuff come in the wrong dimensions, and then i threw it out the window and im somewhat winging it.
i dont think my old thread still exists on endchan, but it had some of my theorizing before i started
specing out a lot of my stuff i did some very rough calcs on things like total weight, torque, deflection etc and i basically just bought well above all those values because i also want to be able to use these components in the future when (if?) i upgrade
i'll just say this about my rails since its what i remember– i had them parallel within a few thou. its difficult to say why they would were off, though i suspect it has to do with some screws not being perfectly straight and moving the rail one way or another when they're tightened. i should have a little bit of play in adjustment, but generally speaking they should be pretty close even without it.