Hi Ray.
Well it certainly is wider than 126mm!
The dropout doesn't quite appear 135mm but certainly is 130 or so.
For a more accurate indication, your rule '0' left end needs to be against the flat where the locknut fits, you can see the nut marks on the flat where you should measure from, just in front of the trimmer setscrew.
Similarly the measurement needs to be horizontal to the right hand flat, where the nut marks will be there too.
The best tool would be calipers with internal gap measuring jaws, I inherited mine from my father who had every tool under the sun!
With that OLN size hub 7 gears cassettes are no problem, freewheel or freehub designs.
My Raleigh was an in-between OLN, but was cold set wider when I had a 126mm hub clamped in and I was hit from the side by a car coming out of a driveway across the pavement onto the road, where I was!
I got his number though.
My left hand pedal came up and took it off the front of the car.
He drove off without stopping, leaving the number plate behind!
All the best,
Robin.