Re: 375 main rods...

I agree with Russ's point. As railroad technology evolved more and more the ability to make field adjustments was eliminated.
There was always a battle between the Mechanical Dept. and the Operating Dept.
Mechanical said that if Operating would leave things alone and show good judgement "things wouldn't break or get out of adjustment and everything would run fine from shopping to shopping".
Operating said that if Mechanical did their job right in the first place "the operating guys wouldn't have to adjust things to get over the road".
Of course there was a grain of truth in both positions. Remember that in the early days the engine crew had the responsibility to "get it over the road no matter what" The old books are full of hints on how to handle breakdowns.
As locomotives got larger it became impossible to keep parts that could be adjusted in adjustment due to the increase in mass and dynamic forces.
Forged end main and side rod bushings are a good example of this evolution.

I hope this helps explain the changes.

John Bush