The Great White Brick - '69 Valiant
We've only been working on the front of the car, not really touching the back half yet. Like you said, don't want to get overwhelmed. When I have time I crawl under the back and scrape off old undercoat and dirt, but we need to work our way from front to back, I suggest you do the same.
The replacement front frame I got didn't fit into the body exactly the same as the old frame. What I mean is, it fit but some of the "landmark" spots I had in my mind to use as line up spots were different! For example, there's a small fold in the frame right at the inner fender, where it folds and suddenly becomes visible at the front of the car, where it continues towards the radiator (under the battery on the drivers side). That part of the frame is painted. Know where I mean? That funny looking fold was in a different spot on the new frame, compared to the one we took out. Different spot by about 1cm maybe. I can only assume it's just a slight difference in manufacturing from plant to plant or day to day, or maybe worker to worker? I don't believe things need to be 100% perfect, just perfect enough that you can get the car aligned, and even then you could put the car on a frame straightener if necessary. Just make sure the front meets the rad sadle properly and that the torsion bar crossmember is square with the body. This is why we put ratchet straps on the crossmember, to pull it back ever so slightly to get our measurements right.
It's amazing how flimsy the body is once the frame is cut out, and amazing how rigid it is once the new frame is welding in. Good luck!