Achieving a perfect fit with Doug's Headers D564 Tempest Long Tube Headers on your 1964-1967 Pontiac GTO, Le Mans, or Tempest involves careful attention to detail. Start by inspecting your motor mounts; they should be in good condition and meet factory specifications. Aftermarket mounts may cause fitment problems, potentially leading to contact between the headers and the frame. Replacing or shimming the motor mounts can help. Next, address potential interference points like brake distribution blocks and clutch Z-Bars, which may need to be relocated or modified for clearance. Carefully follow the disassembly and assembly instructions in the Doug's Headers manual, removing components like spark plugs, exhaust manifolds, the starter, motor mount bolts, oil filter, and dipstick tube as directed. Begin installation with the passenger side header, ensuring proper positioning and clearance. You may need to lift the engine slightly to create space. Secure the header, gasket, and bolts evenly. Repeat this process for the driver's side, paying close attention to any specific instructions related to brake distribution blocks or other obstructions. Once the headers are installed, check for clearances around all lines, wires, and components. Double-check the tightness of all bolts, brackets, and accessories. Reinstall any removed components, such as spark plugs, the oil filter, and the dipstick tube. Finally, start the engine and let it warm up. Listen for exhaust leaks or any unusual noises. After the engine has warmed up, shut it off and re-tighten all bolts. Following these steps and the detailed instructions in the Doug's Headers manual will help ensure a successful installation of your D564 Tempest Long Tube Headers.
