Since I originally posted the question, I acquired several ROM SIMMS and put pictures here:
http://www.flickr.com/photos/gary_w/
I've mentioned this before in other threads...
To accurately track Apple ROMs, go by the numbers on the chips, not the numbers on the circuit boards. While Apple may have done a good job of having distinct circuit board part numbers in the Mac II family ROMs, they often did not do a good job. The reason is that the same circuit board can hold ROM chips with different code on it. So the circuit board only tells you what machines it might fit into, which can be a wide array. The ROM chips tell you what code is present.
Notice that the copyright on the artwork on the ROM circuit boards for the IIfx is 1989, long before the IIfx came out. The same circuit board can be used for many different models of computer.
In the case of Gary's IIsi ROM, it appears to have ROM chips with the parts number 341S0020 through 341S0023. The SOIC IIfx ROM has 341S0781 through 341S0784. The PLCC ROM has 341S0769 through 341S0772.
Incidentally, anyone who has ever tried to figure the revision of a Beige G3 ROM, could save a lot of trouble by looking at the ROM chips rather than the circuit board part numbers.