Mike, Not an electrician but did build my own house, including electrical. I would guess NO, unless you can see how the box is afixed to the trusses(rafters). If it, the box, is just screwed or nailed on one side, chances are that it would be limited as to what it can hold. (a light fixture is okay). If it is screwed up through the bottom (now the top) then there probably is a support piece of 2x4 between the two trusses, which would hold the weight. The box may hold the chandelier "as is", depending on the actual weight, but better to be safe than sorry. The box isn't the issue, it's how it is fastened to the ceiling framework.
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