The bob weight numbers that the crank manufactures list are target bob weights that allow a balance shop to balance an assembly internally without adding heavy metal to the end counterweights------

Now most of them will sell you a balanced assembly, but of course this means that you buy your rods, pistons, rings, bearings from them also---

We also use some Callies cranks that we have them balance to OUR specs for some shelf packages that we stock----keeps them honest!!!!an example is the 414 cid kits for our Dart SHP SBC engines--4.125 bore/3.875 stroke/6.000 rod--and yes the 3.875 stroke is so there is some material in the piston top--

And---the Scat 3.75 crank/6.0 rod packages are good sellers and Corey has several piston confiqs here at all times with what to me seems like a lot of packages coming constantly