"clunk" going into reverse

just checked u-joints and they are good and tight. Do have a question on 8 1/4 and brakes. I have an 8 1/4 out of a Volare (unfortunately I was told it won't fit the Dart)would the brakes off of the Volare rear swap onto a a-body 8 1/4, been thinking of doing an 8 1/4 swap may start thinking little harder on it, and start hunting for one.
Thanks
Aaron