The old motor doesn't need the heads off. The gaskets are fine. And if you do decide to do that you will need new head bolts to put them back on properly as they are torque to yield bolts (aka- one time use). You need LIM gaskets and a replacement upper intake manifold and you will likely have a good spare engine assuming the nothing bent when it hydrolocked.
Is the oil full in the new motor? You didn't mention that. How did you check the oil temp and pressure before you pulled it? These cars don't have a true pressure gauge from factory and no oil temp gauge either. The oil pressure sending unit is located on the side of the oil filter adapter. Check to be sure it's dry and the wiring to it is good. Could be a false reading. If in doubt find a good electric gauge and hook it up in it's place and see what the true pressure is.
From sitting that long I could see the lifters bleeding dry and needing to be pumped back up with oil, which would cause the lifter tick you are hearing. Since the tapping comes and goes, does it seem to show up when the oil light comes on?
