Will a Chevy 305 engine adapt to three speed transmission in your 77 truck it use have 250 inline six?

The Chevrolet 305 cubic-inch V8 engine was not originally offered in the 1977 Chevrolet C/K pickup trucks, which came standard with a 250 cubic-inch inline-six engine. The 305 V8 was introduced in the 1976 Chevrolet Camaro and would not be available in a C/K pickup truck until the 1978 model year.

As a result, it is unlikely that the 305 engine would "adapt" to the three-speed transmission in your 1977 truck, as the engine and transmission were not designed to work together. Additionally, the 305 V8 engine may require modifications to the engine mounts and other components in order to fit properly in the truck, as the 250 inline-six engine is a smaller and lighter engine.

Therefore, it is generally not advisable to attempt to install a 305 V8 engine in a 1977 Chevrolet C/K pickup truck that originally came with a 250 inline-six engine without the proper modifications and parts.