Weird valve/opening at back of lower intake...pcv? (pic)

Looks like what was part of a road draft tube from older engines. They had a steel tube down from that area to the under side of the car to allow any blow by to exit under the car. Before PCV valves were in heavy use.

That's exactly right. That's the top portion of the early 64-65 road draft tube. A 1" steel tube was originally attached to that, and extended down the RH side of the bellhousing to an angle-cut (rear facing) tip below the engine, to draw fumes out of the crankcase when the car was moving. There was also a tab attaching the tube to a bellhousing bolt. Pefectly good system, but pollution regulations changed to require a PCV system to burn these fumes. The tube was only tack-welded at the top, I've seen a number of them come apart as yours has. You could easily make a new tube using ordinary conduit, if you can't find one.

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