Before I acquired this Blazer, it had an intake gasket leak and coolant got into the oil and was driven this way for an unknown period of time. The gasket was replaced and the oil has been clean for a long time.

There is a slight tick that increases in speed upon increased revs followed by low oil pressure when warmed up, but it doesn't sound like a rod knock (knock on wood).

I'm wondering, could something be wonky with one or more of my lifters or Valvetrain which could be causing low oil pressure, and hopefully it's not the rod bearings as previous owner has suspected?

 

Only things that I am aware of that can affect oil pressure are: oil pump and worn bearings both rod and main.
The "tick" you hear could indeed be a lifter gone bad. Have you tried to isolate the "tick" using the "ole long screwdrive" method - hold blade against various places and handle to your ear?

Sorry, but coolant in oil and driven for a period of time almost always means bearing replacement, both rod and mains.