YMMV of course. My old engine had 210k on it, and I drove that thing hard... Always did an oil change before 3k miles, flushed the cooling system at least 3 times a year. No clue how the previous owner maintained it, I put over 40k miles on it in the 2 1/2 years I've owned it. I still need to clean up all the oil and grease, but I can see where the engine restorer clogged up some of the oil galleys

 

Sounds bad with the galleys sludged up.
I've got about 140K on it, I know it sat for about a year before i bought it – I think that is what could have caused the lifter(s) to stick.

Any idea about the oil losing its viscocity?

 

If it sat for that long it probably needs a good douching. I would run some rotella and MMO in it and change every 1k miles until it starts coming out clean, or even a synthetic oil as long as you don't mind dealing with the oil leaks that will surface. You will want to keep an eye on leaks regardless, that old sludged up oil could be hiding some leaks.