66’ style PS box to 72’ style

The steering gear boxes should swap over between the '72 and '66 no problem. In the '66, just use that year's pitman arm, and if you're going with the original '66 pump, swap over the aluminum return line fitting on the control valve. Careful with the O-rings. Hopefully, you have the correct '66 brackets and pulleys for that pump, as the '72 Saginaw stuff won't work with a Thompson/Federal/TRW type pump. What year is the 318 and all it's water pump, brackets, and pulleys? Oh, just remembered that the pressure line on a '66 273 uses a 90 degree fitting on the control valve to clear the exhaust manifold. That can be a little hard to find if it's missing, or, you didn't save it