SUNW,m46B resolutions?

I have a U5 whose framebuffer is a SUNW,m64B according to the ROM code
and, according to 3.1 (that being what's on the drive at the moment -
the machine has sat idle for some time now) is

machfb0 at pci1 dev 2 function 0: ATI Technologies 3D Rage I/II (rev. 0x9a)
machfb0: 16 MB aperture at 0xe1000000, 4 KB registers at 0x00000000
memctl: 003210b3
machfb0: 2048 KB SGRAM 62.999 MHz, maximum RAMDAC clock 170 MHz
machfb0: initial resolution 1152x864 at 8 bpp

How can I tell what resolutions are available, and how do I set them?
On the SS20, I could cd to the device (in OF) and do "words" to get a
list of, among other things, resolution words with names like
"r1280x1024x66".  But on the U5, I don't see anything that looks to me
like a resolution specifier, even with fcode-debug? set true:

ok cd /pci/pci@1,1/SUNW,m64B
ok words
selftest      disp-test     close         remove        restore 
draw-logo     write         open          install 
self-test     set-mode      show-modes    mode# 
read-rectangle              draw-rectangle 
fill-rectangle              get-colors    set-colors    color! 
color@        dimensions 
ok 

I wandered around the Web a little, but most pages I found that talked
about setting the resolution were talking from the Solaris command
line, which of course isn't much use to me.  Some things talked about
"setenv output-device" to set the device.  A few of them specified
resolutions, though they disagreed on how to spell them (some used the
rXxYxHZ syntax, other xXxYxHZ); none of them gave any way to list the
available resolutions as far as OF is concerned.

I poked around the device's words some with see, but either I missed
something or the stupid thing does only one resolution - the device has
a word "show-modes", but it prints just one line:

ok show-modes

2 = 1152 X 900 @ 9450 MHz
ok 

Interestingly, it shows 1152x900, not the 1152x864 printed by NetBSD.

I'm surely missing something somewhere here.  But what?

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