Poor suffering dog, abandoned for so long. Such a little dog for such a big man...
Have you considered tying the Subaru cross member not only to the front A arm pickup point but also to the rear A arm mounts? As I recall the original Subaru intact structure effectively offered up something like that. I know there are lots of things to look at around that area such as exhaust and coolant plumbing that make my offhand comment likely impossible or ridiculous. If you can it offers a way to provide a rigid plane down low to complement the longitudinal structure of the existing car and tie the suspension and power plant assembly together.
I like the idea of the bolt in rear crossmember to open the area for engine removal and a relatively easy means of adding other features to the cross member (easy to create something entirely new if needed if the current solution doesn’t support the rear transmission mount, gear change mechanism etc). You might consider adding boxed flanges on the ends of the rear crossmember to attach not just at the pivots, which is a pin joint and provides no torsional rigidity, but also higher up and bolted to the frame rails or other additive structure.
A large part of what the OE rear structure imparts is torsional rigidity to the rear of the car in addition to being a beam traversing the width of the car to carry suspension and jacking loads. Making an assembly to regain or improve on the existing torque box will be needed once you cut all of that rust and so on out of the car.
Think about the rear structure of the car like a drawer or an open topped box, the top of the drawer is open and in the case of a car with an engine sitting in it so is the bottom. The more you can tie the corners of the bottom of the drawer together, the less likely it is to twist. If you remove a side of the drawer, it will twist easily unless the bottom is very stiff. If you use the engine cross member to tie the bottom of the “drawer” together and ensure the end of the drawer is rigid and equal to the opposite end, transferring the loads across the end you will minimize the twisting imparted by suspension and engine torque.
Perhaps adding a more structural upper cross member above the shelf like the one in an X1/9 or Porsche 914 will assist in creating that box with your bolt in lower cross member extending it.
Ok thats enough Karl blathering on.
Thanks for the video and another peek into your thought process and the convoluted path of changing the car from one thing into quite another. It’s something I have been doing in my mind as I look at my red X sitting in the garage.
