Michael,
  I had to implement exactly the same traps in order to get NuBus
video working. I am not sure about SlotManager routines, I do not
remember the numbers. I also mapped the entire card physical address
space into the kernel. If you know the address range of IIvx video,
you can do the same. I found that the driver writes freely into those
physical addresses, so using some virtual base does not help much.
 You may grab my diffs and sources from
ctpa01.mit.edu:/pub/ivanenko/macbsd_video.XXXXXX.{diff,tar.gz} and try
to adjust them for your situation. (CAUTION: under construction, but
works on my IIcx). I mostly changed grf_mv.c and you need to play with
grf_iv.c, so your changes should be mostly independent from
mine. Ken's colorkit uses essentially the same diffs but older
original sources (as far as I know).

Good luck,

	Taras Ivanenko.