| You can search this forum for threads on acoustic guitar conversions and some good info will pop up.
A classical is not the best platform to mod. Due to the natural tension of silk wound and nylon/gut strings, their tension is much less than a comparable steel string acoustic. What this means is that the bracing under the soundboard is weak in comparison to steel string acoustics and classicals don't have trussrods. The bottom line is that in order to run bass strings on it, you can't use the stock bridge or any bridge that is fixed to the soundboard, as it will create too much tension and will eventually cause the soundboard to buckle - probably dramatically.
If you really want to do it to a classical, you'd be well advised to use a floating bridge with a tailpiece to help break up the tension of the steel bass strings. Personally though, I'd use a little steel string acoustic... | 
