I was surprised that I couldn't find any guide for this, but I figured it out pretty easily on my own. I had a language card I'd scavenged for the last of the 4116's I needed a few years back, but still had plenty of 4164's around.
It's simple cutting two lines and making one wire jumper to convert the board - works great. To change over the one 4116 that comes from the motherboard would take two more cuts and jumpers, so I left that one alone. I can document it if anyone else ever needs the info and can't figure it out.
It would be nice to use the wasted 48k extra RAM, but I'm sure that would require a lot of extra logic.