Ah- I was unsubscribed from the list, so I probably missed a few good
responses, but, yes,the answer seems to be to pull enough of the latest
snapshot to get ofwboot.elf:

ok boot net
Boot device: /sbus/SUNW,hme@e,8c00000  File and args:
Timeout waiting for ARP/RARP packet
Timeout waiting for ARP/RARP packet
Retrying ... Check TFTP server and network setup
Retrying ... Check TFTP server and network setup
4400 Retrying ... Check TFTP server and network setup
15400 >> NetBSD/sparc64 OpenFirmware Boot, Revision
>> (mrg@powerofseven.eterna.com.au, Wed Aug 22 07:29:37 EST 2001)
Using BOOTPARAMS protocol: ip address: 192.67.166.64, hostname: ultra1
root addr=192.67.166.79 path=/space2/root/ultra1
loadfile: reading header
elf64_exec: Booting /sbus@1f,0/SUNW,hme@e,8c00000/netbsd
4701633@0x1000000+134584@0x1800000+4059720@0x1820db8
symbols @ 0xfff0e300 74+319680+170346 start=0x1000000
chain: calling OF_chain(800000, eef8, 1000000, fffb5a80, 18)
[ using 490880 bytes of netbsd ELF symbol table ]
console is /sbus@1f,0/zs@f,1100000:a
Copyright (c) 1996, 1997, 1998, 1999, 2000, 2001
    The NetBSD Foundation, Inc.  All rights reserved.
Copyright (c) 1982, 1986, 1989, 1991, 1993
    The Regents of the University of California.  All rights reserved.

NetBSD 1.5Y (GENERIC) #0: Mon Oct 29 13:39:36 PST 2001
    mjacob@ultra1.feral.com:/tstsys/arch/sparc64/compile/GENERIC
....