Agreed. 20K may be conservative. A rolling restoration may be the way to go in this economy. Brakes first. No discussion there. Brakes first. Then drivetrain. Get the stock arrangement up and running before that big block goes in. Big blocks like gas, if you haven't heard. Then you can get the interior into a condition that you are comfortable with. And then you can look at bodywork and chassis cosmetics. ( assuming the chassis was safe to start with)
Mark and Jon are trying to save you headaches and frustration. I'm trying to save you money (they are too) Don't blow it all apart and not have the enjoyment and use of the vehicle. And along the way you'll learn a bunch. You'll save a bunch. And you'll make some good choices based on experience, not what you thought you wanted. When (if)the economy comes back, you can move on to another project, or kick this one up a notch.
