Then you have to remove the two rack handles (3xscrews each)
Then you have to remove the top cover screws (can't remember how many of them). Once you have removed the top panel screws, lift the panel gently. There's a reverb tank bolted on it, and there's two wires connected to it, be careful not to damage them.
Once you're done, your Quad should look more or less like that
Yup, that cab is a vertical 2x12 Engl cab, with Celestion V30s. Just love it.
As far as it goes for the Intellifex, I liked it alot but had to get rid of it because I had serious incompatibility problems (the Quad's output level was somehow too high for the poor Intellifex inputs ).