I did some experimenting with an old laptop SIMM this weekend - using a hot air gun to pull some of the chips and then stacking them upon others. With a suitable iron, patience, and lots of flux, the second chip isn't too difficult(*) to solder. A third chip however is a bitch, as Shonky has alluded to. It's not even just getting the pins lined up and soldered - the CS pins need to be broken out of the stack. With only the second chip you just bend it up and solder the wire to it. You cannot easily do that when you need to stack a third chip on top - the best you can do it bend it straight out, but now you're soldering a 3D jigsaw with a 0.05" pitch. It adds a whole level of complexity and risk to a project that is already risky. I think I'll stick to 32MB when I do mine.

One issue that I haven't really resolved yet is how to straighten the pins effectively. Even after using an old DIP chip pin straightener to clamp and straighten the pins, they still have a curve to them. Any hints Shonky?

(*) "not too difficult" all being relative.