Many thanks to all for your replies and interesting links!

Things are getting clear now... in order to put over 8 MB on the Macintosh II, I need:

1) The 68851 PMU (which I don't have)

2) Specifically for Bank A, update the ROMs to those of the IIx (or newer...)

3) PAL SIMMs

Issue 1 should make me forget about the others and having over 8 MB on my Mac II ever... anyway, 68851s don't seem to be that hard to get -- who knows!

The II has no ROM SIMM slot, but DIP sockets instead -- even easier to update for me! Although it's a minor issue, I could go up to a reasonable 20 MB (or even 68!!!) without it. Plus, I don't know what the upgrade ROM would think about the installed IWM (instead of the expected SWIM)

Of course, "clean" ROMs are needed for the OS in order to access more than 8 MB, but anyway the software workaround (MODE32) seems fine, so it's a minor issue, I think.

Finally, issue 3 is shared with the IIx, and the question remains: 30-pin SIMMs are relatively easy to buy, but how can I be sure that they'll work on the II/IIx?

All the best,