According to this the Core did proceed down to an antimatter souce.
Produced by Paramount from this illistrator.
Strictly speaking, it proceeded FROM an antimatter source. The top of the intermix--the impulse deflection crystal--is not a deuterium injector, it's a transfer point between the intermix chamber and the impulse engines. As Probert explained once, the entire purpose of the intermix chamber is to connect the matter/antimatter reactor to all the engine parts that will make use of its power. Those same schematics also show an auxiliary fusion generator on S-Deck (feeding into the intermix chamber incase the main reactor fails) and likewise show the reactor itself on U-Deck; THAT reactor at the bottom of the shaft IS the warp core. If you don't believe me, go to sheet nine and read the synopsis for U-Deck where it says:
U-Deck is also known as the reactor deck. The reactor bay holds the main matter/antimatter reactor, twenty four antimatter storage bottles, and the bottom of vertical intermix shaft Engineering Core. Aft of the reactor bay is the retractable tractor beam, flanked by two bussard collectors, which gather interstellar hydrogen, process it, and refil all internal hydrogen tanks.
Apart from basically placing the ramscoop in the main deflector dish (as I always thought it should be) this would also mean the ship's deuterium stores are small to non-existence since at warp speed the ship runs almost entirely on material gathered from the interstellar medium.
Come to think of it, CTM, that's a tricky choice to make once you get to work on the navigational deflector. Especially considering your designs are based on this blueprint, if you put the ramscoop in the deflector, you'd have to flesh out some kind of plumbing system in the front of the engineering hull to route deuterium to where it needs to go.
I get it now.
The The Motion Picture ships weren't using Dilithium to mediate the reaction! If memory serves... The Star Trek Flight Chronology notes that anti-matter reactors existed BEFORE the discovery of Dilithium Crystals. Matter and Antimatter were brought together in an undisclosed method.
So she Dilithium was discovered they designed a system to funnel the reaction plasma Through the crystal.
Eventually the 24th century combined the Dilithium Crystal Chamber and the Reactor vessel. This must be why Warp Cores are now potentially much more unstable.