I returned this one and found the 5V EDO sticks that I successfully borrowed the chips from, as I mentioned in the other thread. Kind of a shame as this one had thin package chips that would be more authentic (and allow for a bit more clearance between the modem card below and the metal shield above).
Kudos to
@3lectr1cPPC because your link to that eBay 24MB module was the reason I realised that my 4MB card's PCB was actually designed for up to 32MB capacities. It has solder pads which act as jumpers depending on which density of chips you are using -- and I was able to change them based on the seller's photo.
I have an Apple supplied 8MB RAM expansion card but I figure that it wouldn't take higher capacity chips, because it doesn't have the jumpers which you can change.
Next upgrades are BlueSCSI and a 540c LCD.