I'm not as good with a schematic as you, but I'd strongly suggest trying a known good A3640 or even a 4000/030's 68030 board. Usually malfunctioning chips will show a diagnostic colour on the screen when the 4000 does its selfchecks. Unless the Kickstart is bad, of course, but that's a lot less likely than the CPU board being bad. If the monitor is getting a sync then the display chips should be ok, otherwise you'd get "no signal", and that also implies you're getting a reasonable +5V line.
Where are you in the world? Maybe someone can loan you a 68030 board? I have one spare but it's at my parents' house 150 miles away....
