I wouldn't recommend powering up the board with those caps if you are at all worried about your components. The uF rating is more important than the voltage in capacitors. It's better to be off on the voltage a little bit.
If these caps are in a circuit that is frequency sensitive, it's hard to say what the difference in uF's will cause. Going from 1600 to 1000 uF is a pretty big difference.
What's it cost to ship something overseas? I've got a handful of 1500uF 6.3v caps lying around, they might be close enough to work...