The upper cross member is just .5"x2.5" flat bar. While very inefficient strength wise laid flat it is simple to bend with a press brake or heat and bend in vise. You can make a cardboard template to use to match bends. 2"x 3/16" flat bar lays flat in the top of the cross member. The thicker material needs a transition to the lighter material to prevent stress risers.
As far as a bolt in top cross member goes the only concept I have seen that is close is a gen 3 hemi and automatic conversion mounts bor B body made by Black Heart? Holley.
The upper side of the torsion bar cross member is cut out and replaced with a 1/2 flat bar hoop that has 3/16 ears that bolt to the original transmission holes. Looks like the lower transmission mount bolts inside of that.To me that seems backwards. If the top half fit to the inside it could be plug welded or something and not move when the trans mount was altered.
There are a lot of different ways and thoughts on how to do these installs. I just wanted to throw some ideas out there.