Back when the Pantah was only a 750 I played with stroking. It can be done safely but is all about correct process. I think I still have some of the weld wire around. Stroking was common back then but the only one I know that still offers this servise is APE
http://www.racecranks.com/ As MikeV mentioned. With such a selection of later model cranks custom stroking would not make much sense.
-Cranky-