I'm with Madmaxx in that if you still have
oil pressure then a good cleaning and bearing swap (done in the car) is feasible. Last year I started to lose
oil pressure and upon inspection of my main bearings had this to look at:
So the bearings were surely going (on a motor with only 10,000 miles at the time) and
something worked its way into the oiling system. The crank was still shiny with no scoring so I swapped out all the mains and even swapped out the connecting rod bearings just to be safe (they weren't even close to showing signs of wear like these mains were). I also swapped in a fresh
oil pump and gently flushed the oil cooler and all lines. This brought my oil pressures back to where they should be and so far so good.
Good luck!
-Dean