I have a 1978 pontiac firebird. I want to know what is the difference between a (408N carrier) posi unit and a GOV Lock posi unit. I am going to be using my firebird for a street/strip use. Something to take to the strip on friday night and if I want to drive to work monday morning. Which one will hold up better and give me the most driveability with the best traction at the track. Thanks.