Almost all the older GM inline engines had progressively larger main bearings going toward the flywheel. That would include Buick, Olds, Pontiac, etc. The prevailing idea back then was that the flywheel/clutch/transmission needed more support from a bigger bearing due to increased leverage and weight loading. In about 5-4-3-2-1 seconds, some "engineer' with no hands-on engine rebuilding experience will tell you I'm full of BS!
Jerry
