Hi,
Maybe you should rethink your engineering: if you spend five minutes before you produce your PCB, then you safe a lot of time later.
I have some cases in stock. And I have the PCB dimensions in my PCB layout software libraries as packages.
It's only the first time when I use a new case to draw a package for the library instead of drawing lines directely in the PCB editor.
Then every mounting hole is at it's place...and the PCB fits perfectely in a case.
The simplest is to use standard PCB sizes. Euro 160 x 100mm, or 100 × 100mm, or others..
Klaus