I've been developing my own master cylinder resleeve kit 1/2"
I did one and one of the members here on the forum has been testing it on his MKlll and all seems to be good
I just did another one for my unfinished 72 Interstate , staticly (not riding the bike) it seemed fine , but I could see that the rubber hose was a big problem, I just fitted a stainless hose, WOW what a difference,
now the end of the lever travels no more than 1" toward the handlebar and just stops. the difference in feel is unbelievable.
In time I plan to offer the sleeve down kit and hose assembly , now here is the problem.
I wouldnt mind doing the resleeve but shipping cost to and from my country the Philippines would be the killer.
owners could fit the kit themselves , which basicly consists of loctiting in the new sleeve and drilling 2 small holes in the fitted sleeve , its easy, but my concern is supplying a "do it yourself" kit and the owner stuffing it up and blaming me due to his incompetence.
Hmmm