Nate,
Use the large wood working clamps from Harbor Freight. They have 2 all-thread rods with wood handles that allows you to clamp odd shapes. Plus they are made of wood and will not hurt the items being clamped. I have a couple you can borrow if you wish.
Rick
That'd be great. Could I grab them at the meeting? I may end up going and getting a couple more as well depending on how many I need.
One more question...being that I'm going to only have silicone holding the pieces together, should I be thinking about a brace or two along the 3' lenght of each side of the overflow?