The official 30-pin DIP pinout does not support double-sided modules (i.e. there is only a single /RAS and no bank select signal). I agree with the previous posters that the chips are 256k x 1, so the capacity of the chips add up to 512k x 18, or two banks of 256k x 9. I guess these modules work at full capacity only in selected hardware that repurposes one of the excess address pins (256k x 9 only needs 9 pins, but there are up to 12 address pins in the 30-pin pinout) as /RAS2, just as PS/2 simms have separate /RAS signals for both sides. Maybe these modules are not compatible to the standard PC memory pinout at all.
As usual with small PCBs that (mostly) contain only traces, you can use a continuity tester to buzz out the connections. Datasheets for 256k x 1 RAM chips in that case are readily available, and RAM chip pinouts are mostly standardized.