Torch for sure. I've done alot of sheet metal work, and for something that heavy you're going to want a torch. A shear on something that thick is not going to give you the cut you want, it "breaks" the metal rather than shearing it. A good throatless shear would cut it, but it would be ugly and you'd end up grinding it to shape anyways. If you took the time to cut the radius's with a drill, then cut to those reliefs with a throatless shear it might look "ok", but metal that thick does really like to cut to any shape other than straight. Just my $0.02, but with a shear you'll have squirels with the cross section of a Stealth Fighter.....funny little facetted creatures:)
Dan