I like where your going with that actually, however, the Dougs headers are only 550$ and they are one of the only headers that fit an a body without dragging on the ground everytime you hit a speed bump, as well as one of the only ones that you dont have to remove all of your steering **** to install/take off, and my city is full of gigantic potholes...i found that lesson out the hard way on my 70 dart a few years back, As for the msd ignition, i dont know why it costed that much for you, you can get a used 6a box for like 100$ and the blaster coil ext for under 100$ the plug wires are only 100$ too.
That being said, the Crate motor sounds like the good route to go, skip all the BS and work and just sign a check and be done.