--- Geoffrey Alexander wrote:
I may later put back one of the two and see if it still works.
--- end of quoted material ---
It would be instructive to try 1MB and 2MB SIMMs.  Note that the RAM bus is
16-bits wide, so you can't just install the SIMMs one at a time.  One would
hope that the LC II, Classic II, and Color Classic are similar, but that is be
naive.  I've scanned the developer notes from Apple on those models, looking
for insight into the RAM addressing.  The note for the Color Classic is the
most complete.  It says 

"The first 10 MB of the address space are reserved for RAM. The actual amount
of RAM installed can be from 2 MB to 10 MB. At startup time, a routine in the
ROM examines the RAM and stores the size in a low-memory global variable. The
Macintosh Color Classic always allows the upper 2 MB of built-in RAM to be
addressed in the topmost 2 MB of the 10 MB address space, as shown in Figure
1-3 on page 6. The system software uses the topmost 2048 bytes of RAM to store
system information."

Also, the lower 2 MB of onboard RAM is unavailable in the 10 MB configuration.

Here's a reproduction of the memory diagram mentioned:

 +--------+   +--------+   +--------+   +--------+  $9f ffff
 |  2 MB  |   |  2 MB  |   |  2 MB  |   |  2 MB  | 
 |image of|   |image of|   |image of|   |built in|   
 |built in|   |built in|   |built in|   |        | 
 +--------+   +--------+   +--------+   +--------+  $80 0000
 |        |   |        |   |  2 MB  |   |        | 
 |        |   |        |   |built in|   |        |   
 |        |   |        |   |        |   |        | 
 +--------+   +--------+   +--------+   +        +  $60 0000
 |        |   |  2 MB  |   |  2 MB  |   |        | 
 |        |   |built in|   |built in|   |        |   
 |        |   |        |   |        |   |        | 
 +--------+   +--------+   +--------+   +  8 MB  +  $40 0000
 |  2 MB  |   |  2 MB  |   |        |   |  SIMM  | 
 |built in|   |built in|   |        |   |        |   
 |        |   |        |   |  4 MB  |   |        | 
 +--------+   +--------+   +  SIMM  +   +        +  $20 0000
 |  2 MB  |   |  2 MB  |   |        |   |        | 
 |built in|   |  SIMM  |   |        |   |        |   
 |        |   |        |   |        |   |        | 
 +--------+   +--------+   +--------+   +--------+  $00 0000

It is of course possible that the LC II is different.  I'll dig up the LC
developer note; the LC II note says that the LC II is like the LC.