You just have to get the angles correct. The hardest is the side holes. The side can be done from either end, the test of the gundriller is if they meet in the middle. Don't forget the relief hole and spring back into the crankcase. Bear in mind you'll need the cam shaft with the groove on the centre bearing and you may need a two piece sleeve or similar to back up the original
oil groove. Also the reverse rotation cranks will have to have the rear main grooves cleaned off as they will try and pump
oil out of the motor.