AFAIK the "Liberation" font in Linux is meant to have the very same "metrics" as Arial. In other words, despite minute differences, replacing one by another shouldn't change anything in the formatting.
Btw, your interest in font metrics make me think that you may be using Gimp for something which it isn't designed for. If you have that much text in your work, you should likely be using a typesetting software such as Scribus (or even LibreOffice).
Btw, your interest in font metrics make me think that you may be using Gimp for something which it isn't designed for. If you have that much text in your work, you should likely be using a typesetting software such as Scribus (or even LibreOffice).