I too used the cj5 bestop bikini, I have the tan version, it fits near perfect, however I mounted mine to the windshield frame slightly different. And didn't need to trim the top at all.�
I used the channels that came with the top, trimmed 1/2" of each piece at the flat end and mounted them to the top of the frame. The curves on the channel match the stock frame, just mounted the snap rivet a inch or so down the side of the frame, a little black silicone under the bestop channel made it water tight, had it mounted for three summers now, never leaked once, including this summers Wet season.
There are two sizes of tops for the CJ5 51 to 75, and 76 to 83, the later is the narrower top I believe. The windshield frames are different widths, I believe I have the narrower top, hence the better fit with no trimming , shame I didn't find your tread a few months ago, I could have pointed you in right direction and saved you a trip to the upholsters. My whole set up cost $50 shipping included.