Chris,
Looks good! I'm guessing your 3D prints are for casting patterns?
On the bottom of the real 25 ton trucks, the spring seats are just symmetrical on each side, and there are cross brace straps that run from side to side. The 20 ton trucks are more like what you are building. Seems odd to me, the 20 ton trucks appear stronger than the 25. Maybe the spring plank was prone to cracking with all the twisting movements, where the straps would flex more...
On your model you may choose to build it your way for stability though. Attached are a couple of drawings I did for trucks for our models. These were done about 15 years ago, and they are missing some details. All this was before consumer grade 3D printers and were intended to be scratch built in a 1:24th scale.
Casey