I am in the process of building exhausts for a CR build, I have bought Swarbrick headers and using spanish made megas. Having used an F1 as my donor bike I had the later flanges and the double threaded studs. Straight forward I thought, just take them out ,get early K spigots and the star head bolts. Totally wrong, I couldnt budge them, I hit them sharp cracks, double nutted them to no avail. After a while I had a brainwave. I got a piece of flatbar, drilled an 8 mm hole and mig welded it to the studs, brilliant they all moved, I simply cut off the flat bar from the studs and removed the stud. Thought I would share my experience, hope it helps someone, regards Kenny