You need enamel or powder cote and it to be baked on a fresh oil free block. It's the porosity of the aluminium cast block that has been soaked in oil for years that pushes the paint off. And if you are going to media blast the bare block make sure it is vapour or soda blasted not shot blasted. And mask off all internal surfaces before you paint it as loose paint inside the block can come off and go thru the oil system and scrap your engine and turbo.