All it takes is repositioning the crank lower rod pin to change stroke.
I am not saying you or I can or would do it, but it really not that hard especially if you could get the outer crank halves undrilled for the crank pin.
People build stroker cranks all of the time for cars and motorcycles.
On race car motors we have added welding to one side of a crank rod surface and then machine the journal back to round but offset to lengthen or shorten a stroke the reharden the crank with heat treating. Over simplifying the process here, but that is basically it.
With a motorcycle crankshaft blank it would be some simple machine work for a factory to move a crank pin and make any stroke that they want...within reason of course, based on crank case room.
These could build you a crank in whatever size you want:
As well as a cyliner in any bore you could want...it just money right. Hey that guy in the other link paid 50k AUD for a Dakar replica....OUCH....I am sure you could build a 97X60 motor for a few grand if that is what you wanted.