Oy veh!
1) As Mark has observed, a submarine can float with just its superstructure above water, and that for sure isn't made of anything lighter than water
2) No one's talking about neutral buoyancy (though a sub can achieve that by careful ballast adjustment)
3) If Mark's experimental float (cane antenna one end, matching steel antenna the other) just floats with a given shot load with the cane antenna at the top, do you really think that it would sink if rigged the other way up? Fact is, it will sit exactly the same either way up.
To reiterate, so far as buoyancy is concerned, the distribution of weight within the floating object makes NO difference. Honest injun.