I had one installed on my 1982 720 that the original owner ordered when he purchased the 720 new.

I sold my 720 frame and i’m not using these U-bolts since my 1983 frame has the brazed on fork bolts for this rack.
You can have these U-bolts free, just pay post.

Also,, do you have the correct length rear Jim Blackburn rack? These were specifically made for the 1982 720’s long chain stays. The one pictured was also purchased by the original owner.