Here's why:
* The 305 was designed for fuel efficiency: The 305 was introduced in 1976 as a smaller, more fuel-efficient option compared to the larger 350 cubic inch engine. A 4-bolt main design adds strength and durability but also adds weight and cost.
* Two-bolt mains were sufficient: The 305's smaller displacement and lower horsepower output meant that the standard two-bolt main caps were sufficient for its intended use.
* Focusing on cost: Chevy aimed to keep the 305 affordable, and the two-bolt design was a cost-effective option.
While you can find some aftermarket parts and modifications to convert a 305 to a 4-bolt main configuration, it wasn't a factory option from Chevrolet.