Chris, Can you clarify which GM 6 cylinders you are asking about? Definite differences between Chevy and GMC (inline) 6 cylinders fuel pumps. There are also some variations for the Chevy, depending on the years and the model/series involved.
If you can give a more specifics on engine size/year, we should be able to help you find the info you seek. Generically speaking, there are two primary fuel pumps for those years. Up to/including 1957 AC 4149 is called for in many of the Chevy Master Parts Books and for 1958-62 AC 4434 was the primary fuel pump. There are a few variations for some specific bigger truck models equipped with air brakes, but these two are the primary models.
One other important note, there are a ton of "off-shore" made wanna-be fuel pumps which have caused a bunch of grief for many Bolters as they are literally inoperative junk out of the box. More info available when you let us know more details on your questions.
