Quoting myself from my book: "If necessary, the mating upper & lower pair of bearing halves can be of sequential sizes (rather than both the same size) to achieve a specific clearance. The Ford factory manuals for the “Indy” 255, “Le Mans” 427, and “Trans Am” Boss 302 recommend this procedure. If you have .001” now and want to obtain .0015”, you don’t have to grind the crankshaft, just use one +.001” bearing half and one +.002” bearing half."
