All good valid points & questions .
Piston oiler nozzles look good .
No funky spray pattern on top of the piston crown .
Keep in mind this is a 290 Cummins big cam 1 . Turbo but no aftercooler .
Not that uncommon to see them " Flame " down the piston skirt .
I'm guessing piston ring failure got it started .
Number 4 failed and # 6 was not far behind it .
Going with rebuilt injectors and keeping the old heads .
This is what happens when ya keep a truck around to long ….. Ya get to work on it once in awhile . LOL !