I do have O42 as well, can't get you those till I get home this evening.
If you get SCARM, it has a grid layout. You draw two lines representing your walls, select mth track and place your pieces. The grid is graduated and will give you measurements, plus there is a measurement tool so you could find out the distance you need to build out. It's really helpful for planning!
Remember not to put the track right up against the wall, I use 1-1.5 inches so longer cars won't rub on the wall when turning.
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