A couple more things for you to consider:
1. Will do use the camera exclusively for AP work? If so, you don't need a replacement glass. That is only done to preserve the refractive index and therefore the autofocusing on your lenses. As you will be manually focusing in AP, it is not vital to replace the glass in front of the sensor.
2. If you still want to use the camera for daytime work, you need to replace the glass (and re-calibrate for WB).
Peter Tan is a reputable supplier of replacement filters
http://www.tan14.com/gears.htm
I done two mods myself, a Baader BCF filter replacement for 40D, I got the Baader BCF replacement filter from Peter.
I recently did a full spectrum mod of a 1100D (removing the front filters but not replacing them with a clear glass or a BCF filter, therefore the autofocus is "out of focus" with EF lenses, but works fine in prime focus). If you go down this path, get a EOS clip in UV/IR filter to minimise star bloat.
Hope that helps!
Bo