I don't know what a "Tubus Classic Evo 28SL" rack is - I think you are mistaken in your description. There's a Cargo Classic and a Cargo Evo, each offered in 26" and 28" versions, the difference being 11-13mm in height to accommodate the difference in wheel diameter.
I had a 26" Tubus Cargo Classic on my 700C Disc Trucker, it fit fine even with Velo Orange 700c x 52mm Zeppelin fender. I recommend the shorter 26" version of the Cargo Classic or Cargo Evo for your 26" Disc Trucker (I prefer the Classic). I know the Cargo Classic fits LHT better than the Cargo Evo model, which interferes with LHT's Breezer style dropout.
https://www.tubus.com/en/products#c405
https://www.bikeforums.net/21622100-post10.html