440 Won't start syndrome

Something is definetly happening out of time! 10 deg BTDC isn't enough to cause a backfire. Bad coil won't cause backfire because it only fires when its told to by the distributor or module. Remember the coil fires all 8 cyls(assuming its distributor ignition) so it wont cause a problem in just 1 or 2 cyls. The fact that its popping back through the carb means you have combustion when the valve(s) are open. Make sure the dist & wires are correct & timing isn't 180 deg off. Adjust as needed. If its got points, make sure they're set correctly. Remember, dwell affects timing. Next make sure you have no mechanical issues like a broken valve spring or stuck valve. Make sure the mechanical advance is working correctly in the dist too.