Anyway I assembled one, with some difficulty because the chips are actually slightly a different footprint - a bit wider! (TSOP instead of SOJ)
It still doesn't work after beeping it out. I was about to investigate further with the diagnostic cartridge, but then I noticed something in the data sheet and think they are incompatible. Just thought I'd run it past the experts here to double check.
I thought they were standard 60ns 4k x 4bit memory chips. However I notice now they are the 4k refresh variant, so I guess A11 would need connecting up to provide this refresh. Now the Falcon only seems to have A0-A10 on the memory bus, as provided by Combel. So pin 6 is NC on these boards.
So... I'm out of luck here right, 4K refresh ram chips are useless on the Falcon?
Edit: Found this, looks like even the row/column number of address bits differ: https://www.ardent-tool.com/memory/pdf/refresh.pdf. i.e. 12/10 vs 11/11. So definitely look like they'd need an adapter with logic to work.