Get a GT650R front master cylinder (not 250 , not 650 naked , not 250 naked) , it must be 650R — Then get XRT Levers (Hyosung Approved) from MotoGB UK (ring em) or Startrights Leeds.
125 master cylinders do not fit custom levers, = why? The master cylinder only wants skinny levers that are exactly as how Hyosung made them. We all tried tbh, some people actually bought some and shaved / skimmed the lever to fit inside , what if he isn’t here ? & died as his lever finally warped. Wouldn’t mess with brakes tbh .
I wouldn’t use universal cylinders = They are 99% rubbish and are not better than Korea’s TCTC brake systems (hence older 650s use the same calipers but bigger master cylinders)