Ther's a main bearing that's used in a Buick 403 engine, and several Olds and Cadillac engines that will allow the stovebolt mains to remain in place and be bored and line honed to fit the smaller bearings. They will serve as reducer shims to allow the same size bearing bores to be used front to rear. The Federal-Mogul part number is 4281M. The bored-out bearing shells will be retained in the block and the cap by flat head Allen screws and red LocTite. The shaft diameter on all the main journals will be 2.498-2.499". That approach will allow the original stovebolt thrust flanges on the #3 bearing to remain in use.
Jerry

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