I received the following email from Mark Huie. In it, he describes how to upgrade the 2M Visor to 8M. Thanks Mark!

Tim,

If you're interested, I've upgraded my standard Visor from 2M to a
Deluxe-like 8M by simply making my memory board look like the 
Deluxe's (upgrading the chip and moving the jumpers around.)

I didn't take that great of pictures (yours are great), but if you
want to post the instructions, I'm sure your page would be a great
resource (as opposed to my nonexistent page).

here's what I did:
I attempted to copy the picture the memory board on

That essentially consisted of replacing the chip and swapping jumpers-
the extra filter capacitor that the 8M chip needed was actually
already on the board.

I pulled the jumpers off positions R17, R21, R23, and R26 and put them
in R16, R22, R24, and R25.  They pretty much are positioned in pairs-
R16 & R17, R21 & R22, etc., the main thing is that the R19/R20 pair is
not swapped.

A helpful hint is that if you're using a hot-air reflow machine, you
should remove the components from near the memory chip before
attempting to replace it or else you get capacitors and jumpers
blowing across your workspace.  I did lose a couple of jumpers, but
merely replaced them with bits of wirewrap wire.  Luckily I didn't
lose any capacitors.

-mark

Parts

See my IIIe/IIIx upgrade page for some sources for the 8M RAM chips.