You're mostly correct.....I would say that, in the case of your car, you can use
any 340 driver's manifold with the JGC 96-98 passenger. I don't know if I would mix a JGC with a stock 318 driver (too much imbalance) but it would work. The 340 driver/JGC combination can be used on any
67 and up A body with or without P/S. The JGC manifolds are plentiful and cheap and you can find one close to your location here:
Car-Part.com--Used Auto Parts Market