Time to get the frame etch out and start checking measurements:
Coupling rod bearing holes come out at 38mm centres, which is dead-on for a scale 9'6" wheelbase, and this matches the measurement for the axle centres on the frames:
Now I did say I would be trying to equalise the chassis using Continuous Spring Beam suspension. On this four-coupled chassis, I want the centre / fulcrum point of the leaf-spring beam to be above the level of the hornblock guides. Looking at the chassis frames as supplied....
....this could be a problem, because the low top line of the frames means there's nowhere to install a fulcrum. In an ideal world, the topline of the frames would continue straight through where the letters "T M D" are, instead of dipping down.
'tis time to improvise......