Al,
when i was digging around learning about spectroscopy, I found this info on christian buil's website.
http://www.astrosurf.com/buil/baader/eval_us.htm
Basically it shows the std 350d uv/ir filter blocks out "almost everything" ! A modification using the baader filter will improve responses in the IR end, but the uv end still has the major drop off. Certainly taking out the filter altogether will greatly improve the overall response of the ccd chip.
It's an option I've looked at occasionally: modify a dslr or go for a true b+w ccd.
My initial decision is to go for a b+w ccd as the bayer matrix will also impact on the responsiveness / resolution of the system.
cheers
Mark