Two reasons to paint the inside of the blocks, especially BB Mopars if you have used a grinder to deburr the casting flashes inside those blocks. The paint will seal the pores and trap the microscopic pieces that were ground off and imbedded in the block. The second thing is for oil return, especially on any motor using a stock small capacity pan like most small blocks and a lot of the pre 1967 BB. or any motor that has 4 quarts and is drag race and revved above 5000 RPM. I like using the 1970/1971 stock Mopar 6 pack and street hemi oil pans, they hold 6 quarts in the pan and, depending on which oil filter you're using whatever amount of oil it will hold. On BB you can drill all the small depressions in the lifter valley where oil will pool to make sure most of the oil drains back into the oil pan, I'm not talking about half a pint or more, I'm talking about maybe 3 to 6 ounces at the most:soapbox: but every drop in the oil pan is available to be used for lubricating:icon_fU::thumbsup: