Are those large objects on the crank counterweights for the pistons/jugs?
Those are the crank lobes. Yes, counterweights in a manner of speaking. The piston clamps between the lobes.
With respect to the cases/bearing shells, you would use your crank, pistons, and piston bearings. But you need to confirm using Plastigauge what main bearing shells (crank bearings) you require. The Plastigauge is bought at the auto store, you drop a dab under the crank, torque the crank into the case, release the crank and measure the width of the dab. That tells you the bearing thickness you need.
You can locate the bearing IDs on your case at the rear of the case, stamped into it. If by chance the letters are the same on yours as the new set, you're in business. If not, you need to do the plastigauge to purchase and install the correct shells.