Break in gone bad... 360

I have no idea what the op ran for timing and would sound kinda lame telling him he needed more or less timing.
Too little timing and it fires late and makes the motor the hot , too much can be hard to do without any load on the motor...but things arise from too much if not adjusted on the mixture end.

Dry stems pulled the seals up, can happen, usually the seals just burn and then the guides suck oil. I have seen the wrong seals used and them riding the stems.
The dark rings...oil rings ,well ....you did say it smoked just before shutdown...so I bet A. the intake manifold gasket leaked and sucked oil from the valley... or B. You have a ring problem in those 2 cylinders.