The early 250 Extra Large does have Showas, or at least same make as 750..
difference being, the length of the slider, they even accept 72 and earlier disc brake hanger I believe (or part of it), but it is in the wrong place.., I think axle clamp is different.. but I think parts of the patterns were used on both forks
Your only problem really id the distance of the grroove from the top surface of the fork leg..