You should grind on the crank over the case b/c you don't want to risk losing the seal around the crank in that area. When the cranks broke by the induction port I think it was mainly due to the edge of the hole being too square or sharp edged, so all the stress was located in the weakest spot where if the corner was radiused more would be stronger. Also making sure the intake ports on sleev all open at same time instead of one side sooner than other will make more power then also making sure all the ports open straight or square instead of from one end to the other or however. On .21's though you have to be careful with if the ports open square or tapered from one side or center out b/c the ports are bigger than on .12's and the piston can catch on them, especially exhaust port.