Jim,
Standard problem with all works drawings - they're 'intent' rather than 'custom and practise'...
It's not helped either that General Arrangement drawings for diesels rarely show the external details of a loco so they need building up from framing drawings and panel outlines. Even then it's tricky to replicate the effect of the 2lb lump hammer when the parts don't quite fit, or the bit that old Fred removed from the panel stamping to get it all to work together.
I'm minded to draw comparison to the EMD F-units. All built to a common set of drawings and parts, yet it's possible to discern repeatable differences between those built at La Grange or at London.
Steph