you could be right on the silver vs black.
if i remember correctly my U bolts are from my first rebuild project. i bought 3 totaled cuda's in 1975 for the enormous sum of $250. i then used parts from 1 car to fix the other 2. after they were repaired i think i sold them for $1500 each. the U bolts were in a box of parts i found in storage. things might have been mixed up over the years, maybe someone worked on the car before i bought it. all i know is the cross hatch pattern on the inside of 1 U bolt is different than the other 3. when i found them all of the U bolts and nuts were in 1 plastic bag just as i removed them in 1975.