I stumbled recently upon the data sheet for a MOS 6545 CRT controller and MC6845 CRT controller chips.  I noticed that the vast majority of the sync-related registers map identically to those found in the 8563 VDC, which leads me to believe that the 8563 has a 6545 buried within it.  So, if I start out building a 6545 clone first, I should be able to build the VDC in terms of the 6545.

Most importantly, the datasheet provides the timing diagrams I needed to understand how the vertical total adjust and such works, as well as how the internal counters work.  H and V character counters are up-counters as far as I can tell, while "display" counters seem to be down-counters.  All these extra counters I was needing appear to be functionality that is VDC-specific, and not CRTC-related at all.  This is good to know, because I can factor functionality into more manageable pieces.

So, before I replace the VDC's CRT controls with those from the CGIA, I'll give the VDC one more chance, now that I know the foundation on which the VDC is built and have a datasheet for the 6545.

(I still think it's overly complicated, and I still think the CGIA's approach is simpler.  However, I'd prefer to maintain as much compatibility as I can.)