After I decided that I need to tear off the entire front end I decided I needed a chassis jig to keep things square and give me a level measuring plane to weld the new parts back in the correct position. I'm a Mechanical Engineer so I took to my schooling and designed something I thought should do the job. I knew I needed to control four points per side per factory mustang chassis drawings, for a total of eight supports. I designed some trusses and thought a lot about how it would assemble and how it would work with the restoration. Went through many sketches and decided on a design. I then ordered up a bunch of square tubing and went to work in the fabrication bay at work.
I ended up with a bolt together frame work that turned out WAY better than I expected, especially considering my experience welding thin wall steel tubing was lacking. I just considered this needed experience before I jumped onto welding on the actual unibody.
Here is what I came up with after about 60 hours of fabrication over 2 or 3 weekends. The main structure is 1-1/4" x 0.065" wall tubing with 2" x 1/8" wall main supports. The two uprights attach to the front leaf spring mounts and the forward bar with the scissor jack is at the front of the rockers. This allowed me to pivot the car around the leaf spring mounts so I could adjust the front suspension mounts to the proper height off the measurement plane which is the top surface of the trusses.
Here is one of the four perpendicular trusses clamped down to keep it from warping while welding. Overall had to think about the sequence to clamp, tack, and weld to keep from warping.
Since I made most of it from thin wall tubing with bolt together joints, I had to TIG weld in crush sleeves into the holes. The main welds were with MIG. I used 1/2" grade 8 bolts, IIRC, with 5/8" tubing sleeves.
Next step was to get the car on the jig. First was to support the front by jackstands and the back with a cherry picker. Note that the closest side truss had to be placed throught the cherry picker leg prior to lifting. The side trusses were set into place and loosely bolted. Not shown here is setting in the four cross trusses and bolting everything up.
Next was leveling the jig with shims down to the concrete. Once the top surface was generally leveled, tightened all the bolts. Next step was to dial in the shims to get a good level measurement plane on the top surface.
Next I adjusted the scissor jacks to get the car to match the prints on all the suspension and rocker measurements from the factory drawings I found online. One note is that one common drawing online is completely wrong. Once I figured out the right angle, to get the measurement right, I put two more scissor jacks under the front of the front frame rails and welded in some fixed uprights to the rear leaf spring mounts.
In the end, it turned out to be a pretty rigid structure! I can push and prod on the car and nothing shimmies or budges.