Why couldn't he just add RTC function to the Pi and why the heck isn't a Real Time Clock built into the Pi? :
This guy made it work on a Pi. Reading between the lines I think the guy doing the Beaglebone writeup missed the fact that the Pi does have some hardware acceleration built into it that makes this possible (if slightly awkwardly) and instead concentrated solely on doing the bitbanging *entirely* in software. He made it work on the Beaglebone by using the PRU, which is a fully programmable co-processor, not just a "real time clock".
Strictly speaking the best way to drive a Mac CRT from a Raspberry Pi would be to leverage its built-in "DPI" (Display Parallel Interface) support. This is mentioned in passing in the article I linked above (he misspells it "DPM".) The advantage would be that by using it you don't have to make make software understand you're using some weird "fake" framebuffer that's being bitbanged out via ad-hoc methods, you'd have something that looked like an "official" according-to-Hoyle framebuffer that at least in principle works with X11, etc, directly. Here's an article about how it works in general, what math you need to do, etc. That article is about making it work with TTL LCDs, but it's pretty flexible. Here is a VGA adapter that can use it, and all it uses for parts is some resistors. Here's the document on the Raspberry Pi website that discusses the software configuration for setting up hsync and vsync
timings for non-standard resolutions, which of course you'd need.
My first crack at Googling up someone actually following through with this idea to drive an old Mac monitor hasn't panned out, but I'd kind of be surprised if nobody's done it or something like yet.
Doesn't look like grayscale, one wonders about that possibility?
Not without modifications to the analog board hardware. (The internal grayscale cards for SE/30s accomplished this by replacing the board that goes on the CRT neck.)
Of course, these ideas for driving it with a Raspberry Pi don't really help if the goal is to use it with a PC server motherboard. Honestly your options there just aren't very promising. There was a project (links to it are somewhere on the forum) for using a small ARM board to convert the CRT into essentially a USB-driving framebuffer you can drive from a Linux computer, but it was pretty involved and could only manage single-digit FPS screen refresh. (Which might be fine for a server.) Your best bet really would be to chuck the original guts and mount a 9" monochrome VGA monitor in its place.