I built an install iso and, hey, it worked!  I can't say that I'd throw it
into production tomorrow, but this is sorta cool.

# dmesg | more
console is /pci@1f,4000/ebus@1/se@14,400000:a
Copyright (c) 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004
    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 2.0F (GENERIC) #7: Tue Jun  1 17:40:28 CDT 2004
        
peter@zipper:/usr/peter/sparc64/obj/usr/src/sys/arch/sparc64/compile/GEN
ERIC
total memory = 2048 MB
avail memory = 1993 MB
bootpath: /pci@1f,4000/scsi@3,0/disk@0,0
mainbus0 (root): SUNW,Ultra-4: hostid 80b15697
cpu0 at mainbus0: SUNW,UltraSPARC-II @ 400 MHz, version 0 FPU
cpu0: 32K instruction (32 b/l), 16K data (32 b/l), 4096K external (64 b/l)
cpu at mainbus0 not configured
cpu at mainbus0 not configured
cpu at mainbus0 not configured
psycho0 at mainbus0 addr 0xfffb4000
SUNW,psycho: impl 0, version 4: ign 7c0 bus range 0 to 0; PCI bus 0
DVMA map: fe000000 to ffffe000
IOTSB: 32a0000 to 32a8000
pci0 at psycho0
# uname -a
NetBSD  2.0F NetBSD 2.0F (GENERIC) #7: Tue Jun  1 17:40:28 CDT 2004
peter@zipper:/usr/peter/sparc64/obj/usr/src/sys/arch/sparc64/compile/GENERIC
sparc64
# uptime
12:25AM  up 1 min, 1 user, load averages: 0.32, 0.18, 0.08
# df -k
Filesystem  1K-blocks     Used     Avail Capacity  Mounted on
/dev/sd0a    15107878   335928  14016557     2%    /
kernfs              1        1         0   100%    /kern
# ifconfig -a
hme0: flags=8a63<UP,BROADCAST,NOTRAILERS,RUNNING,ALLMULTI,SIMPLEX,MULTICAST>
mtu 1500
        address: 08:00:20:b1:56:97
        media: Ethernet autoselect (100baseTX full-duplex)
        status: active
        inet 12.30.65.29 netmask 0xfffffff8 broadcast 12.30.65.31
        inet6 fe80::a00:20ff:feb1:5697%hme0 prefixlen 64 scopeid 0x1
hme1: flags=8822<BROADCAST,NOTRAILERS,SIMPLEX,MULTICAST> mtu 1500
        address: 08:00:20:b1:56:97
        media: Ethernet autoselect
hme2: flags=8822<BROADCAST,NOTRAILERS,SIMPLEX,MULTICAST> mtu 1500
        address: 08:00:20:b1:56:97
        media: Ethernet autoselect
hme3: flags=8822<BROADCAST,NOTRAILERS,SIMPLEX,MULTICAST> mtu 1500
        address: 08:00:20:b1:56:97
        media: Ethernet autoselect
hme4: flags=8822<BROADCAST,NOTRAILERS,SIMPLEX,MULTICAST> mtu 1500
        address: 08:00:20:b1:56:97
        media: Ethernet autoselect
hme5: flags=8822<BROADCAST,NOTRAILERS,SIMPLEX,MULTICAST> mtu 1500
        address: 08:00:20:b1:56:97
        media: Ethernet autoselect
lo0: flags=8009<UP,LOOPBACK,MULTICAST> mtu 33136
        inet 127.0.0.1 netmask 0xff000000
        inet6 ::1 prefixlen 128
        inet6 fe80::1%lo0 prefixlen 64 scopeid 0x7
sl0: flags=c010<POINTOPOINT,LINK2,MULTICAST> mtu 296
sl1: flags=c010<POINTOPOINT,LINK2,MULTICAST> mtu 296
ppp0: flags=8010<POINTOPOINT,MULTICAST> mtu 1500
ppp1: flags=8010<POINTOPOINT,MULTICAST> mtu 1500
strip0: flags=0 mtu 1100
eon0: flags=3<UP,BROADCAST> mtu 1500
        address: 00:00:00:00:00
#