. I guess milling the piston would keep it close to stock stroke.
Little clarification: Piston or rod has no bearing on the stroke, to change stroke you must change the location of the rod journal, bring it closer to the centerline ofthe crank and decrease the stroke or move it away from centerline and increase.
Also, longer rods GENERALY are better because, it raises the angle of the wrist pin in relation to the stock agle of the rod allowing less side load on the piston, also makes a longer lever to turn the crank.
Good luck!