Croft, I got 20 bucks that says his problem is not a stretched cable!!
Another 20 that says once the inside is fixed, he will be able to use the original cable !!!
with 10-12 mm of cable sheath length adjustment built into the cable, coupled by the adjustment at the clutch lever I bet the cable will snap before it stretches anymore then that!!!!
Also I read thru the post and other then having him check alignment of the actuator arm to see if it was located correctly. I do not see where anyone told him to adjust it there. I must admit If from the picture he posted it it looked like the crank arm was in the wrong location verses the alignment mark on the lifter shaft spline I would have had him adjust it correctly before moving on. And while I had him adjust it I would have had him once again with his hands rock the actuator arm back and forward so he could see and feel how much and where the free play is.