I've been looking into the same thing myself and i've discovered that they started the reverse rotation serpentine systems i think in '82 when they started the whole 5.0 HO engine line. I believe the difference is until '87 they were continually changing the impeller diameter of the water pump, but i'm not sure exactly what years they did that but i know that there's at least 3 different sizes, the sizes increased through the production years. I've been looking into putting on a '87+ style water pump, but i don't know if i have to get the whole front timing chain cover (don't know if they changed mounting depths, or ???). It is frustrating because i know for a fact that the '87+ water pumps flow better, but i have no idea how you can retrofit them on an earlier stang. There's a infinate amount of info on everything else, but nothing about the water pumps, which is one of the most important items on the engine. I'm also hesitant to get underdrive pulleys because i don't know how well my smaller impellered water pump would do. I hope someone can clerify this for us...
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'84 Mustang 5.0 LX
My car