http://www.fishandtips.com/index.php
Try that site. You enter the dimensions of the tank, and they give you plans for a stand.
If that doesn't work, all I know is that you want a lot of vertical support, and you want the weight spread out both along the top of the stand (so there aren't pressure points on the aquarium) and along the bottom of the stand (so there aren't pressure points on the floor).
Another option would be to get a storage container from Walmart, Target, or similar store, attach the filter to that, and then you can take more time to either fix the 20g or build a more attractive stand for the 80g.
Good luck. Let us know if you need any other help.
PS. Remember to keep the original filter media wet at all times during the move, so the new tank will be cycled.