The different exhaust stack is the difference between flame dampers and no flame dampers. Some Mk VIs had each kind.
The Merlin 25 was rated for +18lbs boost. There is no difference for 1943 or 1947. They are both powered by Merlin 25s.
The first TR.33s were converted Mk VIs. The one tested is, IIRC, one of those converted Mk VIs.
As to the prop, the main effect that had, IIRC, was low speed acceration. De Haviland didn't go with four bladed props on the Mossie after testing them in 1942 as the effect was not significant.
The navalized equpment would only add weight and make the TR.33 slower.
Yes, that is a FB.Mk VI with Merlin 25s and flame dampers, just as in AH.
An example of a different aircraft is the A6M3 and A6M5. Same exact engine, but the A6M5 had ejector stacks and the A6M3 did not. The A6M5 did 353mph, the A6M3 did 332mph. Now, the A6M was a light aircraft so it will have more effect, but to claim there is no effect when there are many documents saying otherwise is silly. De Haviland claimed the flame dampers reduced the top speed of the Mossie by 10mph or so.