The back fire makes me think the wires are still off. Or something in the ignition is wore out or corroded.
Check the coil wires and the coil ground. Bad grounds will make the timing all over the place.
I would go over all the wires again amd make sure the firing order is correct for that car motor and year. Just to be sure its not an odd firing order.
Did you replace the cap rotor and wires or just clean them up.