Can you hook a v8 up to 4.3l Chevy automatic transmission?

No, you can't directly hook a V8 engine to a 4.3L Chevy automatic transmission. The transmission's bellhousing, torque converter, and internal components are designed for the much lower torque output of the 4.3L V6. A V8, especially a performance-oriented one, produces significantly more torque, which would quickly overwhelm and destroy the 4.3L transmission. You'd need a transmission specifically designed to handle the torque of the V8 engine you're using.