Replacing the fan with an electric unit will not throw your camshaft off balance.
I've found most cases of backfiring out the carb is caused by valve timing or a lean mixture. Replacing the timing set should have cured the valve timing, if that was the problem. Your crank hub may have spun, giving you inaccurate timing marks to begin with. You can check the timing marks on your harmonic damper [balancer] with aid of a piston stop. Check your induction system for vacuum leaks.
Pull the vacuum advance hose off the distributor and plug the hose. Start the engine and adjust carb for a smooth Idle around 700 RPM. Attach a timing light, set the timing to 12 deg. BTDC. Readjust the carb if necessary. Rev engine to 3000-3200 RPM and observe change in the spark timing. Should go up with the mechanical advance, if so you know that is working. Return to idle then reattach the vacuum advance hose, the timing will go up to about 19-24 deg, if you have it on a manifold pressure port of the carb, depending on the advance can and the amount of vacuum you have available at idle. The idle speed should also increase. If the idle speed and timing do not increase, remove the hose from the carb and check if you are getting vacuum at idle, if not you have the hose attached to a stepped vacuum source. Attach the hose to a manifold vacuum source, that is a source that has vacuum at idle with the throttle plates closed. The idle speed and timing should increase with the hose attached to a manifold vacuum source, if not your vacuum can may not be functioning. With the mechanical advance working and the vacuum advance working you should get a total advance of between 29-50+ deg. Before I modified my distributor I was getting 9 degrees base, plus 20 degrees manifold plus 20 degrees vacuum for a total of 49.
If you're valve timing and your ignition timing are all working properly you may be getting a cross fire at the distributor due to a cracked cap or a cap with a carbon trail enabling the spark charge to cross from one tower to another and fire the wrong cylinder, similar to plug wire crossover which you should have eliminated with the new wire set.
Since you've changed the timing set, distributor, plugs and wires and still have the same backfire problem you had before, and assuming the new equipment is installed and functioning correctly and you have no vacuum leaks, I would say you may have an internal mechanical problem such as a camshaft with worn lobes or a spun crank hub. Or perhaps a carburetor or fuel delivery problem.
