Who did Chevy sell the 350 to?

Chevrolet (Chevy) didn't "sell" the 350 small-block engine to anyone in the sense of a single transaction. The 350 cubic inch small-block V8 was and is a GM engine. GM used it in many of its own vehicles, including Chevrolet, Pontiac, Oldsmobile, Buick, and GMC trucks. They also licensed it to other companies. Therefore, there's no single entity that can be named as the recipient of a "sale."