You could try a SBIG CCD
Shameless promotion aside....I'm staggered you are seeing such serious vignetting with a KAF8300 chip.
This should not be the case with a 14" RC.
I'd suggest you'll need at least 36mm or larger apertures throughout the entire imaging system to keep it at bay (1.25" filters, unless very close to the focal plane, won't cut it)
Reflections also look troublesome....they will not flat-field out.
Flocking and perhaps a shroud around the truss may help keep the weird light arcs subdued.