In doing some research I find that the 3986330 was used on the RH side of 74 Z28 L82's (this site and others) but also read some info that the 330 was used only on early 74 cars. What was used on late 74 Z28's?? I have an HEI/ST-10 car. Also is there any interchange differences between a 3986330 and a 3959562?? If I need a 330 but use a 562 to install headpipes will a 330 swap in later without fuss??