I have a pair of NOS U-bolts for sale that fit a lot of the 50's and 60's GM cars. If your are unsure if these are correct for your vehicle just ask me and I can look it up in the parts books. Basically they cover all the late 50's to around 1970 cars with the U-bolt style retainer. These will NOT work on cars that have the strap with 2 fine thread bolts that thread into the yoke. 

Asking $20 for the pair including the mailing cost anywhere in Canada. (Mail cost is about $3)