65 Barracuda daily driver

It doesn't sound like the oil was really low, like not even reading on the dip stick, so maybe that did not cause a problem. The lifter not pumping up sounds like the problem, but I'm no expert on hydraulic lifters. Aren't the lifters new? Could it be defective?

On the intake water leak, what do you attribute that to? Is it possible that the metal pieces that you added to block the heat crossover was lifting the intake off of the head enough to leave a space? Did you use sealant around those pieces or wherever the leak is occurring? Did you do dry test fitting of the intake and measure the gaps at the front and rear "china" rails to see if you needed a gasket there or not?

Just take one problem at a time and give yourself time to figure it out.
Hope you have a nice Christmas and can get your project running well again.