I would test for voltage drop from positive battery to engine block and see what the voltage is there when cranking, then take a pair of jumper cables and go from battery negative to engine block and see what the voltage is then.
Battery cable once overheated or blued do not pass current correctly anymore. It will ohm out fine but doesn't pass the current needed also I have seen more than one bad OEM battery cable that had corrosion once you cut back the plastic protector. It looked fine when you disconnected it from the battery and visually examined it but didn't find out it was bad until it was cut apart.
I agree, double check timing and both advances working correctly. It could also end up being a starter also.