You need the double hump trans crossmember as stated, but you also need to get an engine crossmember because the straight 6 has a rear sump pan and the crossmember is farther forward. I don't know if you already know this, but if you don't hopefully this will help you some wasting time bolting in an engine that won't fit properly. Good luck man!
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'84 Mustang 5.0 LX
My car