you are correct, the fast ratio arms are longer than stock (by 1 1/2" iirc) and they only work with the 73~76 centerlink. the fast ratio stuff doesn't play nice with most headers-- or at least anything off the shelf that i know of.
if you're having clearance issues with the stock arms, a 73~76 setup clears up a bit more room, as JD noted as above.
