No adapter is needed to bolt the grand to the crank. You just have to make sure the back of the crank can accept the trans into it. This is called a pilot hole. A bushing goes inside of it.
When you balance a crank, you also balance the rods, pistons, rings & bearings, damper & flex plate or flywheel. Some shops I know also want the torque converter as well along with it at the same time.
All 273, 318 & 340 engines are internally balanced. (Except a '73 - 340 engine but that can be changed) all 360 engines are externally balanced. LA & Magnum engines have different external balancing weights.