Assuming you have the original front end, You'll need a brace to fit the 33mm forks on a '78 to '80 CX500 Standard, Custom, or Deluxe (thru '81). The '81 and '82 Custom have 35mm forks, so that brace would not fit.
The teleflex/telefix brand I believe...I have seen some where the allen bolts are on the front face...basically two Lshapes with adjustment for fork space via the allens....
If i can resurect the pic will do...