Jackie at Nashville Engine Parts used to be the lead salesman at Grooms Engines before they sold out to a yankee outfit and the quality control went to pieces. I've done business with him for over 30 years. The shims are optional, used as necessary to establish the right main bearing clearance. I like to insert a small piece of shim stock between the bearing shell and the crankshaft, and check the turning effort at the flywheel. When the engine will turn with a slight drag with a .0015 shim under the main bearing, the shim pack between the main cap and the block is about right. Use a check shim about 1/4" wide across the full length of the bearing. Don't forget to remove it after you find the right shim pack! There might be a different shim pack, or none at all, for each individual main bearing. Drop me an IM or an email when you're ready to assemble the engine, and maybe we can get together so I can show you the procedure.
I aviod the "leak at the joint" problem by rolling the seal about 1/4" in the block so the parting line doesn't line up with the place the cap meets the block. Problem solved!
Jerry
