Main bearings + options for coating. drilling, or both. For near stock rebuilds I recommend factory style non coated but drilled main bearings. In any engine I am building no matter the power level I use coated and drilled main bearings. For race engines or high horsepower I use the "H" drilled and coated main bearings. Coated bearings provide an additional margin of protection in a low oil pressure situation. Drilled bearings provide additional oil to the crank and rod journals. If using drilled bearings you should lay the top bearing half in the block. If any of the block protrudes into the bearing hole the block must be clearanced with a die grinder till non of the block is showing thru the bearing hold.