We have scaled the model down for an 8 inch woofer with excellent results.  I have seen many people scale it down farther but you'll have to find them for the results.  

With regard to woofer selection, you generally want to find drivers that will perform well in smaller boxes, sealed or ported.  Look for drivers with an fs under 40Hz and a QTS under 50 (lower is better) and you should have a good results.  Assuming the first two parameters can be found, the next most important one is efficiency.  Higher is better.

Steve