Interesting. Did it start life as a No.4 or a No.5, or maybe a little of both? The bolt knob is hollowed out, so that could have come from a No.5. What's the highest number on the ladder sight? If it's 8, then the sight is also from a No. 5. But then, there are no little No.5 lightening cuts on the upper sides of the receiver, just below where the rear sight folds down, so...
I don't see anything stamped on the left-side flat of the action, but is there anything stamped on the left side of the heel, apart from 'ENGLAND', or did Santa Fe grind that stuff off?