[DanEC]

ERAs have trailing arms but they are dual purpose. The differential is mounted in a cage that is secured at the top by bolts to the frame that act as pivot points. The trailing arms are adjustable and allow tuning of the placement of the wheels fore and aft in the wheel wells and some slight adjustment in differential pinion angle (although I've not read of the adjustment being used for this). Even through the cage pivots the trailing arms still act as locating arms to the frame to positively locate the hubs fore and aft due to road stresses and impacts. Very slick arrangement and I hope I'm not mis-describing Bob's (ERA) engineering intentions.

The lower Jag control arms are pretty rigidly mounted to the differential but I would think there would be some deflection from wheel impacts and loads. If you fabricate and install trailing arms for a fixed differential situation, IMO they should be adjustable in length so you can fine tune them to the differential/control arms position.