[Destroyer]

I completely argree with RWilson.. Don't cut it if you don't have to. The come-along is a great idea. You might also want to try a lot of metal wedges driven between the tank bottom and the hull. (Splitting wedges would be perfect). Just don't put all the force on one wedge. Tap one a little ways in, then another next to it, etc etc etc... that way the force isn't concentrated on just one area of the hull. Let physics do the work for you.

As an aside, as far as cutting goes... if you must cut it just fill the tank completely with water, then drain a little out... it's only the fumes that explode and by filling it completely you force all fumes out of the tank. Then attack it with a sawsall. The metal blade won't spark on the aluminum, so the job will be easy and safe. But by all means try and get it out in one piece first.