B&w Matrix 800 Cabinet constuction

No! You need to know the exact mid drivers and tweeters plus a schematic of the crossover. 

The complete crossovers are availe reworked and the mid range drivers are same as 801 series would have to substitute a tweeter, Im worried about the matrix bracing layout.

Hard to tell what good this project would be. You are honestly far better off starting a new kit from scratch from Madisound, Meniscus or http://www.troelsgravesen.dk/

Whatever you build now won't sound like an 800 anymore, and will be a complete DIY build in a new form factor with new drivers and crossover, so unless you are rebuilding an 800 and going to search for replacement of the rest as a DIY project this is a losing proposition.  However, if you want to start a new DIY project (which you should!) starting out with one of many well designed kits is going to be far more satisfying and worthwhile.

Thanks for sharing the link. I really enjoyed. It was also a lot of work to update my account so I could post this little note.