yesw, you're right, the goshawk was abandoned in 1935, so no steam.
as alternatives, i would have thought the peregrine, after all, it was used in the whirlwind, which was to the same specification,
i would have thought that the merlin was too big, initially, though maybe in later marks, for reasons of growth, and/or commonality of production.
also agree about the flush exhausts, or again, if peregrines were used, the same type of exhausts as on the whirlwind.
i'm not sure about the bubble canopy/cut down rear fuselage. my guess is by the mid-years of the war, the 313 would have been phased out
of production in favour of spitfires.
cheers,
Robin.