Orange replacement swinging arms are very expensive. I’d try it with the original swinging arm first.
For your info’ I’m running 27.5 on my 26″ Nicolai – they actually fit better. To explain, the chainstay is shaped to accept a tyre but when I use 26″ the tyre isn’t big enough to go in there meaning at its widest point the tyre sits at the narrowest point of the chainstay. However, with a 27.5″ it sits in the shapes area perfectly. Additionally, it’s only 5mm higher at the bottom bracket and even on full compression the wheel is nowhere near hitting anything like the seat tube etc.
That said, it hardly feels any different toe 26″ so makes me wonder what the fuss is about.