If it just beeps then it's most likely a RAM issue and maybe just a case of swapping the memory out.
here's apples beep codes
* 1 beep = no RAM installed
* 2 beeps = incompatible RAM types
* 3 beeps = no good banks
* 4 beeps = no good boot images in the boot ROM
* 5 beeps = processor is not usable
.
The unit that starts up but has no display might have dodgy vram installed, maybe an idea to pull that and then try it. If it's a quadra 840av then getting the mainboard off to gain access is a pain in the butt
I'd love to see some pics of the Nubus board
