query on IIgs models

[who@where.what (Bart)]

In a totally unrelated thread Wayne Stewart said: 

>I don't feel the ROM 3 was really an upgrade. Things had reached the
>point where Apple was forced to include a memory with the ROM. So it was
>cheaper to just build it int the computer. Of course once an engineer has a 
>chance to redo something, he is bound to fix and improve a few things.
>I've wondered if the ROM 4 was an official project or a personal project
>of the engineers that went on till someone higher up noticed? 


Which brings to mind a question:  How many "ROM 4" machines are out there?  How 
many known, released, ROM 4 boxes still exist?  Are they all the same or, are 
there  known engineering changes between the various ones? If so, what?  What 
are the major difference between a standard ROM 3 and a ever so un-standard ROM 
4?  Are there any "ROM" differences, ie, was the firmware the same or enhanced? 
If the later, has it been archived anywhere?  
Do any schematics, engineering notes, drawings parts specifications for the ROM 
4 exist?

Related but even more obscure:  Does anyone know where the motherboard for the 
ROM 4 (and even the 3) were "FAB"'ed?  Sometimes the specs on a board can be 
discovered in the back room file cabinets of a fab factory. 
just curious...
-Bart