So, that's why you kept asking. I think this works very well as an opening, but I'd make two comments.
Firstly, I don't think Hattersley would characterise his opponents in so bald a manner ("dinosaurs" etc). Other commentators might (Kaufman, say) but Hattersley is generally much more generous in retrospect, and wouldn't have used that sort of language. And Hattersley absolutely wouldn't yield the mantle of socialism to his opponents - he is a socialist, views and has always viewed himself as a socialist. He might attack them then and criticise them in retrospect as unilateralists (though I'm not whether Shore was), as anti-Europe, as soft on Militant; but not as "dinosaurs" and even less so as socialists. Also, Peter Shore was not an unreconstructed lefty, or at all easy to pin down. Shore flitted between the various wings and factions, without any single base, and usually just with the effect of pissing everyone off. I think Heffer would have done better than Shore, incidentally - at a guess, maybe Hattersley 55%, Heffer 30%, Shore 15%.
Secondly, I'd like to see some quote from Cook (who, I agree, would inherit the leadership the soft left if Kinnock died) to the effect of deciding to concentrate on the deputy leadership and support Hattersley for the leadership (the opposite of OTL, where they concentrated on the leadership). I can well imagine Cook making that decision. Also, Dunwoody and Davies would still be in the deputy leadership, probably doing a bit better than OTL by picking up votes from right-wingers who refuse to vote for Cook (while Cook in turn would peel some left-wing votes from Meacher). So perhaps Cook 58%, Meacher 25%, Dunwoody 10%, Davies 7%.