I have a 72 Grande also!
I bought it from some guy and it had a vinyl top that made the car look like it had a receeding hairline, so I took it off and welded up all the holes.
My engine shudders also and has no power. I was told the engine mounts needed to be changed and that is why it does that. I have yet to check them. That sucker sure is a gas hog!
I'm selling that sucker as soon as I get my truck running!