:crap: I dunno, only seen one thing similar, back in the '70, a friend with a '63 Split, he built a SB for it, and had something in the casting at fault, I dunno what the symptoms far as magnetic shit in the pan/plug, but the block was defective.....
I would pull the pan and chain cover at this point, pull some caps and see who's home....:search::gurney:
Edit, Karsten, is that a FACTORY roller design or aftermarket toggle types?? if it's the toggle types...I bet that's the issue...it's been posted a few times as being troubles like that....