Actually, the first time I had an idea there might be an issue with the bolck was when i pulled the oil filter tree and saw the check valves rather than block offs. Pulling the check valves was a bit of a trick (drill out the end to release the balls and springs, then pound a small screwdriver between the block and valve housing to deform it enough to pull with needle-nose pliers). Best to do before doing engine work so the metal shavings are thoroughly cleaned out of the oil passages.
