Projects Mocking up rear suspension for my Bantam - opinions please

FWIW
I have had a parallel 4 bar on the rear of my car since the 70s. Initially I used aircraft heim rod ends which transferred a lot of road noise.. I then changed too rubber bushing ends using Chevrolet track bar ends.
As far as using outside frame parallel torque arms, I don't recommend it. A very good example of the problems of this set up can be obtained by bending a piece of wire in the shape of a U. With this shape, you can visualize the binding encountered using parallel torque arms. Use one end of the wire to represent one side of the torque arms and the other end to represent the opposite side trailing arm. now, raise one corner of the wire which represents the rear end housing. You will note the wire is ridged and does not allow articulation. Bend the wire enough and it will break,

 

OP, if it were mine I'd stick with your plan you defined as using your existing ladder bars, angled, and coil overs set out wide in your light bantam. Rubber or better poly bushings in the front will certainly give a bit more in articulation and not be as harsh on your backside. The panhard you had mocked up is exactly how I have mine in my triangulated ladder bar '32 coupe. I run all big heims in double shear but I built my glass bodied rod as a brawler. S&W Racecars 42" "gasser" bars with solid heim option. I also run a spool and 125# QA1 16 way adjustable coil overs. Hardcore, yeah OK. Honestly... it's not so bad at all save turning tight corners in crowded parking lots. Street driving is no biggie IMO. Rides fine on soft sidewall cheaters with the coil overs. Going around a traffic circle I notice a little body roll or turning tight into my garage stall but the heims only allow so much. So I don't drive tight corners aggressive like a fool.
If your bars are slightly too long for going directly to your tranny crossmember consider building beefy mounts up off of the front side of the crossmember and have them tie into the crossmember and frame rails diagonally with multi-holed, double sheer ladder brackets. That's how I'd do it.
My car originally had a triangulated 4 bar. This proved entirely inadequate even with the addition of a drag-style anti-roll bar as the rear suspension would twist (i.e. G-body shuffle) requiring a ton of preload on the right rear to level it out on a hard leave.
I didn't catch if you plan on racing this car at all, a lot, or just having the look and cruising it but if you figure since you are building it now it might be good to know it could do it properly if you asked it to perform.

 

4 better ride -Rubber bushings for sure. Worried about cornering - not watts but build a "mumford link". That will keep you busy - lay it out full size with cardboard and dowel sticks. Mumford is series of rods and links from side to side. One side down ( lean in corner ) pulls other side down. "Tea baggers" ( sports car ) love it.... A wee modern for HAMB???