If you've ever seen a house being moved, you've witnessed extensive efforts being made to make sure that the home's foundation is replaced with massive beams designed to ensure the structure can be lifted without any distortion of the home's framework. Even distortion of just a few inches could cause substructures within the home to no longer fit properly.

Walls could crack. Doors wouldn't open and close correctly. Cabinets might pull away from the walls and ceiling. It probably would still be livable but the details just wouldn't be right anymore.

A '72 Demon might not be as complex as an entire home but the same principals apply. As Muscle Car Restorations of Chippewa Falls, Wisconsin, prepared to replace the rear framerails and rear crossmembers, they first built support braces, welded to the frame table, to solidly support the rest of the unibody structure both front and rear. Jig posts were also fitted to both locate and support the front and rear frames from underneath.

While it might be possible to replace the framerails without going to this extra effort, the details might not be right anymore. The doors might not close cleanly, the trunk lid could fit unevenly, and the whole car might not track straight down the road. You could drive it but it just wouldn't be or feel quite right.

As we've said before, it's critically important to install whatever extra bracing is necessary to ensure that no matter what part is removed, the others around it stay put. In this case, since the entire bottom of the car must be removed, that support must come from above as well as below.

This job might look especially intimidating if you walked in right in the middle of it but, if you get all the prep work right, it's not really as scary as it seems.

See all 16 photos Before any work begins on the car, jig posts are placed under the framerails, front and rear, and a pair of "halo" braces are constructed, again over the front and rear, to provide support from above. Additional braces are usually added across the door openings and anywhere else as needed to be certain the body stays completely rigid while it's being rebuilt.

See all 16 photos These are the parts that make up the rear foundation of a '72 Demon — framerails, front and rear leaf spring mounts, upper rear crossmember, and the rear crossmember.

See all 16 photos If you're replacing rust damaged framerails, you're also replacing the floor so MCR will typically remove the floor first thing. This obviously makes it much easier to move in and about the car. Note the pair of jig posts at both ends of the framerail. These will be the primary locating points for the new rails.

See all 16 photos MCR never just casually hacks away at the old parts just to get them out of the way. Careful thought always goes into the process to be sure that all the reference points needed to precisely fit the new parts are preserved.

See all 16 photos The wheeltubs will be saved and will provide solid reference points for the floor. The rockers need to be replaced but they're left in place for now and will help position each framerail.

See all 16 photos Even though the rocker panels will eventually be tossed, they have to be cleaned up for now, so the new front leaf spring mounts can be temporarily fitted to them to position the front ends of the framerails.

See all 16 photos The AMD framerails are very precise reproductions of the original parts. MCR can count on the openings in the bottom of the new frames (AMD #895-1067-L [R], $379.99) to perfectly fit on the jig posts positioned by the original framerails.

See all 16 photos The rear crossmember (AMD #870-1067, $229) is a straight-up bolt-on but leaving the tailpanel in place helps to confirm the exact fit.

See all 16 photos The exact position of the upper rear cross member/shock mount (AMD #860-1067, $239) can't be determined until the intermediate floor is set onto the framerails, but it needs to be at least clamped to the rails to ensure that the frames are vertically aligned and correct distance apart. Once the floor is welded to the frames, the crossmember's location can be adjusted as needed.

See all 16 photos The upper rear crossmember can be eyeballed in place by referencing its position on the original frame.

See all 16 photos After the floor is in place, the upper rear crossmember/shock mount can be positively located by running bolts through the shock mount holes that then pass through the floor to the inside of the trunk. Lightly snug up these bolts, and then the crossmember flanges can be clamped to the frame before welding.

See all 16 photos The front leaf spring mount (AMD #865-1067-1L [1R], $49) fits between the framerail and the inner rocker panel and provides additional vertical support and also confirms the frame's lateral position. This mount will eventually be a reference point to help locate a new inner rocker panel.

See all 16 photos This is a really great view of the relationships of all the parts. It's clear to see that once the framerails are properly placed, the rear floor sections would be fairly easy to drop in place next. Note that this wouldn't be possible if the rear of the car weren't first fully supported by external bracing that's welded to the frame table. We've said this before but it is imperative that adequate external bracing be installed to guarantee that none of the car body can move even the smallest amount while this work is being done.

See all 16 photos Sheetmetal screws and clamps will hold everything in place until the floor sections and any other related parts are installed. MCR will not do any final welding until everything is mocked up and exact fit has been verified.