2448379 main bearing

Not sure what your talking about. But if you are refering to the #1 main bearing upper shell being different then the other mains for chain oiling.
Don't know on the big blocks, but on the slant six the #1 upper main shell (OEM bearings only) had a 45 degree champher on the edge of the shell for chain oiling. Us slant six people, just use a file to add this champher to the bearing shell, as aftermarket bearings don't have it, and OEM are not available.