I made my own clamps, but some crash derby guys have found some cheap clamps here. They are actually shackle straps but can be used as a clamp bracket. You cant beat the price, add in your grade 8 bolts in your needed length from any hardware store.

http://www.etrailer.com/Accessories-and-Parts/TruRyde/TRSL350.html

IMO, you have nothing to lose by trying some clamps first. Easy and cheap. I think 5 clamps would be enough. But Id buy enough plates for 6 clamps.

So you would need 12 plates @ .75 = 9.00
12bolts,nuts if by the pound, ??--= 5.00