From Computer History Wiki
So, it appears that there three (at least) different kinds of ARM10:
- MIT-AI's second moby was apparently an ARM-10, but it was very definitely different from the ARM-10L (one of which MIT-MC had);
- The ARM-10L: there's an image of one the CHM has/had (image here; inside here);
- Eric Smith's KL was reported to have an "Ampex ARM10 external memory box, which provided four megawords of ECC-protected semiconductor memory (using 64K DRAMs) [which] attaches to KI10-style memory busses via the DMA20 memory bus interface" (definitely different from an ARM-10L, which was a core unit)
There nothing about Ampex memory in the Ampex folder at BitSavers, and Web searches turn up very little too.