how stong is a 1800 box??

I have a good 1800 box but as I want to put it behind a wrx motor in a max fx i was wondering what is the weak link in the box?? What should I replace in it or should I just wack it in as is.

kombi boxes are pretty stong you'd have to give it a hiding tro break one in a light car such as a manx
check out this site good gbox info
http://www.geocities.com/Baja/Dunes/9702/transtalk.html
marcel