The thickness is indicated to be 1/10th of an inch.
I think that's the size without an actual chip on it, though. From the description, it calls this an adaptor, and I don't think it's sold with DRAM attached.
It would certainly be a tight fit in an A3000. If you only needed 8 megs, though, you could probably use banks 1 and 3. That would leave quite a bit of space.
