I can’t tell from the photo if the flange is different from the 2x3” Tech IV/V/70 flange, but the seller can confirm the format by looking at the measurement which is printed on the edge of the groundglass, just out of legible range in the photo.
You might try and search on the net to see whether 2x3” backs are interchangeable between the Tech III and later models and if you don’t get an answer, ask BobS, who used to be a rep for Linhof and knows such things.