If I may add a little

With support of what both the Johns have stated and if I may inject a little more from my point of view
The K-37’s will always be stiff in the curves as the trail truck axle center is about 14” farther back than a K-36 The curves are what they are , "tight", and the engines are monsters.
At that point 14" farther back the swing of the trail truck still has to be limited to what the buffers and draw bars can deal with. This forces a lot of goofy things to happen in the front half of the engine with respect to a K-36.
And it also accounts for all the welding repairs to the K-37s frames under the fire box and Busted trail truck springs & rigging
This also explains the track movement out ahead of the engine in soggy roadbed and the busting of rails.And the difficulty with the centering device on the #1 drivers
As John B stated we never did the hole running gear & spring rigging in the 1990’s at C&TS . I did ponder what might out to be done differently with respect to the K-36’s when It finally received a full overhaul.
The K-37s and the K-36’s are basically the same locomotive running gear back to the #4 driver. As I remember it the spring equalizers between #3 & #4 drivers are a little shorter on a K-37 also.
Jack