I did 2 CB750 cafe' bikes here for local riders who bought the Benjie seat-tank combo, and one bought a fender as well. Not a single piece fit, nor worked as intended. At least one of the bikes cost the owner more for my time (at $10/hr) to modify the Benjie parts to fit without breaking themselves than it cost him for me to rebuild his engine to 836cc, complete with valve job. I spent all of July and 3 weeks of August last year, trying to find ways to make the Benjie seat/tank combo fit on that 750K5. In the end, I installed a gel-cell maintenance-free battery, because it takes 30 minutes to remove the seat to reach it: such is the design and quality of those parts.
Since then, I have turned down 3 more full cafe' builds where I was asked to do Benjie "kits". Honestly, I can't spare the time.