2nd stage identification, please?

Looks like the faceplate has been lost. I expect that has no influence on function, and is just an aesthetic issue. LDS hooked it up to a tank and pronounced it a-ok. But I'd be interested to know just what Sherwood regulator it is. Your help is most appreciated.
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SN on the top is R611089. 1st stage, not that I guess it makes a difference, is SRB5900 (Blizzard?).
Thanks!
Sorry about the links. Embedding from Picasa didn't seem to work right for me...

I'm by far not a Sherwood expert; but we have several of them (various generations), and I have the service manual for the SRB5X00 (you can download it here).

It's for sure either an SRB5700 Oasis or an SRB5900 Blizzard. Those both had grey second-stage housings like yours; the Brut and Magnum had black housings.

As far as I can tell, the only difference in the Oasis and Blizzard second stages were the finish of the lever and adjustment screw inside -- both were silver in the Oasis, and black Teflon-coated in the Blizzard. You should be able to see the lever through the mouthpiece.

Looks like the first stages of both the Oasis and Blizzard were identical -- matte finish (vs. shiny for the Brut and Magnum), with two HP and two primary ports.

How can you tell the nomenclature of the first stage? I've got an SRB5300 Magnum, and there's no model marking on it that I can find.

Thanks Marek. Very helpful stuff to go on.
I can tell what the 1st stage is because it actually has SRB5900 laser etched on it in between two of the ports. Adjacent to a serial number.