Thanks. I did the MC88920/88916 swap, and pull pin 9 high (?) or something like that.
http://homepage.mac.com/schrier/q605_40.html
on one machine but could never get video. But I think my VRAM is too slow. There's a note about sometimes needing 80ns VRAM after the 40 MHz upgrade. I've set it aside for several months though (hmmm, I guess it's been almost two years actually. Sigh).
But I've always wondered why the straight resistor swap won't do the trick. Schrier's page says it doesn't work, but it also doesn't say that anyone ever tried it with the clock generator/buffer swap. It seems to bear more experimentation. One of these days...
Hmmm. I just looked over the 88916DW70/80 datasheet and reread the speedup instructions. I wonder if I pulled pin 9 of U17 high, or if I pulled pin 9 of the DW88916 high? I can't remember now, but I think I may have gotten confused and done the latter....