A description of the shark memory design could be found at http://www.research.compaq.com/SRC/iag/info/dnaext/dnard/info/sdram.html (all DEC / compaq links here are localy mirrored, as the original pages vanished, see this article explaining what happened.)
After trying about ten different modules I found only two that got recognized by the shark as 64 MB each. Unfortunately they did not work together:
Virtual address already used screen not found. Can't open input device. Keyboard not present. Using com1 for input and output. DEC,DNARD, 00:00:00:00:00:00 , 128 MB memory Open Firmware Built February 25, 1998 17:19:25 Copyright 1997 FirmWorks All Rights Reserved Unimplemented package interface procedure ARM Forthmacs version F.0 Copyright (c) 1988-1997 FirmWorks Copyright (c) 1993 by H. Schwalm ok
The PAL code on http://www.research.compaq.com/SRC/iag/info/dnaext/dnard/pal seems to indicate the RAM area could be 128 MB, and the firmware detects this amount - but unfortunately does not work in this configuration.
The working modules are called SY8464V and equipped with eight HY57V651520 chips (four on each side).I ended up using one of the above 64MB modules and a 32MB one:
DNARD Rev. 5, 08:00:2b:81:62:5e , 96 MB memory Open Firmware Built February 25, 1998 17:19:25 Copyright 1997 FirmWorks All Rights Reserved Send a line break to stop the booting process. Boot device: /isa/ide/disk@0:\netbsd.aout Arguments: [ no symbols available ] Copyright (c) 1996, 1997, 1998, 1999, 2000, 2001, 2002 The NetBSD Foundation, Inc. All rights reserved. Copyright (c) 1982, 1986, 1989, 1991, 1993 The Regents of the University of California. All rights reserved. ...