I recently purchased a ROM 01 Apple IIgs with the intention of using it to further my disk image explorations. While it came with an Apple 1MB expansion card, I quickly realized that it would be useful to have more memory installed.
In searching for information regarding the memory expansion capabilities, I came across the postings outlining the RAMGS expansion boards from http://gglabs.us/ In it, the developer notes how it is possible to use FPM DRAM in place of the standard DRAM chips. I realized that these same chips are those used on standard PC SIMMs.
Analyzing the circuits used by GGlabs, and comparing the memory portion to that of a standard SIMM, I realized that some simplifications can be made. In particular, the SIMM multiplexes four CAS and four RAS signals to select the byte being read, this means that one of the dual 2:4 decoders can be eliminated by feeding the correct inputs into a single 2:4 decoder.