Using the following plugins:
Zerbu_Outline (to remove the default text outline):
Galv's Message Background (To enable a custom message background)
Using SV.exe I found the message boxes are split up into many files, this was because they can expand to fit the text, I'm not sure how to do that yet, so I just print screened and edited a four line one using dosbox and paint.net.
The Sierra font is a recreation by Goatmeal, who made the font in Quest For Infamy, he kindly made this available online: