I went through this exact issue with my Boss Frog double hoop bar years ago as well a relative's with the same roll bar. I did this writeup but it is now screwed by Photobucket but I'll see about recreating it with a new photo host.
http://gearheadsmiataclub.net/vB/sho...-for-roll-bars
Basically, I unbolted the seatbelt guides, rotated them forward and had them welded in place. That way, the belt strap did not bind in the opening anymore. Also, it looks like your foam padding could use a little trimming as it looks like your belt might be rubbing on it. I had the foam pads too and trimmed them high enough so that they tucked inside the vinyl covers.