Just a bit of info that may help. First the water valve...
The vacuum operated water control valve mounted on the right inner fender may be the most difficult piece to find in good condition today. They tend to leak water after 40+ years of use. I have seen NOS on ebay before but the price is outragous.
I think it could be repaired but I have yet to find anyone willing to attempt the task.
The under dash vents for this model was all chrome plated metals. The majority of those are severly pitted today.The louvers rotated on tiny pins that were easily broken.
Want some positive info ? In 1973 that vent assembly changed to all black plastic. How it attached to the later model plenum changed also so the entire assembly is not interchangable but.. the 4 little vent assemblies are indentical and interchangable
You could buy good used plastic vents from as late as 76 model, send them off for vacuum mettalize chrome plating and you're golden.
One more... The lower dash pads were 68 model only and only 2 pieces unless the car has factory a/c. In this case a small 3rd piece of lower dash pad covers the bottom outer edge of that under dash vent assembly. Those are hard to find in good condition also.
They are easier to restore than the leaky water valve for sure.
Hope this helps and good luck.