The throws on the I6 crank are 180* apart, so a bob weight is not needed. The crankshaft alone is spun and weight is removed or added to the counter weights to give it a neutral balance. It is done on a balancing machine. The pistons and rods are weight matched to the least weighing one as are connecting rods. The connecting rods have to be weight matched on each end. You can do the pistons and pins your self if you have a gram scale, and some form of grinding device. If you have to remove a lot of weight form a piston you can shave the pin end a bit. That pin then must be kept with the piston it was weighted with. When I say a lot of weight, it isn't really that much but the aluminum from the piston weight so little that you have to take out a lot from the piston to match it. The connecting rods can be done using the gram scale, but you would need a special tool to balance each end.
When you drop your parts off at the machinist ask him to show you what he uses to balance these items. Usually they are willing to give you a quick walk though at least. I have been at my machine shop so frequently that I watch the machinist do a lot of things, occasionally helping him. They let me do my own work there if need be and have given me a part time job in doing mechanic stuff. Yeah... I spend a lot of time there.