Well, the two structures I'm describing are visible on both the C model and the later modification used for the Zhukov and Yamaguchi.
Damn, my mistake - the two short strips on top of the saucer, yeah. Those would offer some additional aft coverage, although there'd still be a proximity shadow just below and to the aft where neither the saucer nor the pylon phasers could reach. It wouldn't be more than a few hundred meters long, though - and the tiniest roll maneuver would expose a ship trying to make use of the shadow.
Personally, I'm happy with the E-C being somewhat half-finished, without a ventral transverse strip, while I assume all the later Ambassadors
had this in the Trek reality (since we see it firing in "Emissary") even though it ain't there in studio reality. And I think the forward torpedo position at the base of the neck is also a foregone conclusion, again supported by "Emissary" IIRC.
The one detail I'm not decided on is where the aft torp tube might go. I'd be happy with just one big mother, but perhaps that sort of advanced tech is reserved for forward arcs at that time? The best place might be somewhere in the curve of the fantail, where there are small greeblies plus a row of square plates.