Intermittent misfire (308).

Maybe some experts will have a more substanciated opinion, but it does take quite a lots of misfires to wash the cylinders. As far as the crankshaft is concerned journals form that era are bulletproof.

It does take quite some abuse to damage the lower portion of the engine (by contrast cylinder heads and timing do require some care).

 

As noted there would have to be alot of fuel dump going on, occaisonal misfires would likely have a very small amount of fuel that would boil off through the engine heat and would cause no adverse effects. Even a diluted oil would still lubricate the crank journals with an oil film, they are not subjected to the very harsh conditions of the cylinder rings/bores.

Protracted excess fueling can dilute the oil and wash the cylinder walls causing bore/ring wear. A compression check would help determine if this is the case.