Mine has two stickers on the inside showing the Power-amp tube layout, and they other showing the preamp tubes. One is stuck to the chassis, and the other is stuck to the preamp tray (screwed on the top part of the case). Both of those stickers say "SVT-HD" on them. I posted some pictures in another skunkworks thread, I think it's titled SVT-HD tube functions I think..
Also, if your amps face looks like the skunkworks, but the upper front part of the case is not cut at a slant, then it's the MTI version I believe.
There may some other key things to look for, but I don't know what those would be, maybe transformer numbers?
Hope that helps.