The projection on the bogie stretcher and bogie frame stretcher are part of the original design from Martin; they have been part of the core design since it was released and to be fair, there hasn't been much wailing and gnashing of teeth over the years that I'm aware of, so it must work for some.
It's left in the instructions because it's still part of the etch work. Until a revised set of etches or another form of pivot point is developed then it really has to stay in there, otherwise builders will be left unsure of what to do.
The front end of the Pacific Coronation is impressively tight, as are most Pacific steam engines, the W1, A4 and Bulleid light Pacific are no exceptions and indeed the King and Castle class with their inside cylinders are also very tight.
Our problem (modellers) is that we are pushing the engines to their maximum curvature, on the real thing they will do this, but more often than not the wheels will impact the frame or specially designed expendable rubbing plates, we can't allow that as it'll generate a short.
Therefore there will always be a compromise, where or how the individual chooses to do that is their prerogative.
Our aim (Finney7) was always to reintroduce as much of the range as soon as was reasonably practicable. After that it would be new models and looking back at the range, with a view to tweaking them here and there using the benefit of experience and today's modern building techniques.
In which case the Princess Coronation bogie may come under review, is the current pivot point satisfactory, can it be improved, can the improvement be implemented without recourse to a whole new front end. These questions and many more we do not have the answers to...yet.
My advice would be to leave the pivot point and stretcher extensions in place and try them, you may find everything works fine, you may not, if so then you can begin to explore alternative arrangements.
The front bogie is a mini kit in it's own right so is quite complex, the only other part that might come close is the backhead, have a good look at Richards as he has some nice tips on layering the approach so that you do not end up trying to pass pipes under ones already fitted. Again like the bogie and the Bulleid backhead, it is a mini kit in it's own right.
Mick D
Finney7