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.