I agree it has a lot of features that look very "Stevens". The only thing that strikes me as unusual is the shape of the cast shoes which I cannot associate with anything.
It should not be forgotten that Stevens & Sons just slipped gently out of the business at an unusually early date and many other contractors would make something very similar to what a particular railway company had been using all along - the best example perhaps being Scotland where the Railway Signal Company were producing Stevens-type frames well into the BR era. In the case of the NER, the Northern Division had been pretty loyal to Stevens, switching to McKenzie & Holland upon their demise. And, as has been noted, McK&H certainly supplied some Stevens-style frames for use in gantry boxes where their own product wasn't suitable.
If this frame is on NER territory, looks like a Stevens Ground Frame ("Ground Frame" was the official term) and has McKenzie & Holland locking on it then I think that should be taken as being exactly what it is.
I have another NER "Ground Frame" puzzle to throw into the melting put soon but I won't distract things here with it.