Thank, guys, for the additional information. I thought about the line of sight, too, but then there are all those ships that don't have it, from Zephram Cochrane's Phoenix to the Raven.
Since the process got rushed for TNG production and no impulse exhausts are seen, they could be on the underside of the upper wing, inside the large opening and on each side of that central aft structure, since it's the driver coils that matter with impulse, and the exhausts are just to vent by-product, nothing to do with Newton's Third Law.
And about the large opening, it looks like a good place to clamp down a captured enemy ship, rather than towing it with tractor beams, in which case the "head" might swing out of the way left or right if necessary to allow entry of a large starship, assuming those two large tunnels between main section are hinged that way.
Besides, Vulcan ships have a large ring, and nobody complains about wasted space.
Also, if the Warbird were crippled and upable to limp home under its own power, four shuttles clamped to the flat deck in that cavern perhaps could at least get it moving.
In conjuction with figuring out the impulse, etc. of the Warbird, I also have this one to touch up and label, which I obtained from a zany Cardasian who claimed to have downloaded it from a Romulan computer, although I have been advised to question its authenticity, that he's considered "a FLAAAAAKE."