Well Dave beat me to it with some good info. Here were my ideas.
Wow, tough questions:
1. Would love to replace the O27 switch that allows engines to escape from the red to blue with an O42 switch.
Maybe, but because the curve part of an O42 is wider than an O27, you might have to push the red-to-blue switch farther down the red track to allow the "curve back" to meet the blue track. But doing that would shorten the tail track for engine escape. A better alternative might be to move the left-most red-blue crossover as far left as possible and put another (opposite) red-blue crossover at the other end of the straight track (just before both red and blue tracks follow the curve). This actually lengthens the engine escape, but a major drawback to that idea is that it shortens the existing double-ended red-blue siding.
2. Would also like to find a way to have engines scape from the purple track to the blue without using the mainline.
The only way to do this requires another set of switches to connect purple to blue. Unfortunately, the distance between the two seems to narrow for the switches you are using to work. However, some brands of manually operated switches might work to achieve that goal, but switching track types comes with its own attendant problems.
Lastly, I just looked at your plan from a "reach" perspective. I hope you can walk all the way around your plan with ease for maintenance issues; otherwise, it's sure a long reach across that yard.
Chuck
