Another vote for firing the engine briefly. Is this a stock 318 or did someone (your brother maybe) go thru it previously? I'm usually all about working with what you have but in this case, if you're going to put in $ to redo the engine, I'd seriously consider finding a running 360 and slide that in. Nothing against 318s but, if you can add 42 more cubic inches for the same cost as doing the 'teen, I'd be looking for a 360. You say you have a junkyard next to your work so check with them - maybe they have a good running 360 in a wrecked car/truck? Regardless of what you do, you are going about things in an organized and methodical manner. Good on ya! Keep the '67 Plymouth shop manual - as mosleyme said, the Barracuda was an offshoot of the Valiant product line and they share most common parts.
What part of the Great PNW are you in? I'm in the Cd'A/Post Falls/Spokane area if you are close and ever need an extra pair of hands.