no takers, sorry I don't have the information either. But it appears the perfect radius should be smaller for the exhaust rockers, than the inlet. I have read on anothr forum, some people have used a car adjuster with a ball joint, elephant foot. Porsche, VW and older Merc used these. The thread was very close to the thread on Triumph's I think they are the same as Norton 26 tpi I think?
That set up is the ultimate for reducing valve side wear.