Regarding the extra window ahead of the wing issue - it was a standard feature that the 800 series (i.e. BEA/BA's 802/806 fleet) only had ONE window ahead of the props but had a wider forward door. The improved 810 series (this includes all 81x, 82x and 83x variants - they're all 810's really) had a narrower door and the extra window.
The exception to the rule was I think (as mentioned above) the 833 which had the wide door/single window of the 800, but with the other improvments of the 810.
Interestingly, with the single window 802/806 BEA/BA fleet, the single window ahead of the props was placed slighly differently between the 802's and 806's - it being slightly further forward on the 806's.