71 440 build ? grooved bearings mains and rods

The top shell has a groove that goes up and tapers away about 1/4 of the way up each side of the shell... The grooves in the mains reduce the load capacity of the main bearings by giving that space to oil flowing to the rods. If you have sustained high rpms, they (and wider clearances) are needed. If you're just drag racing and running up to 6500 - they aren't.