Wind chill doesn't affect cars like it does people - it relates to how fast the
wind takes away body heat. On a car it only means that exposed parts get to
atmospheric temperature faster, not colder than atmospheric temperature.
It DOES mean that the radiator blind, cardboard in front of the radiator, etc
is a VERY good idea though. Low temps will probably thicken the oil in the
dampers. Backfiring can be the result of poor vaporization which results
in a perceived leaner mixture. A bad exhaust cam lobe will do it also but
in this case it doesn't sound like it. I had a bad case of it in my 164 once,
and found that an old brittle aircleaner had broken up and pieces of it were
holding the carb piston open. Somewhat past time for a change. Might be
worth checking that your pistons are coming all the way down.

That brings up a question about the dampers - I would think that the pressure
would perhaps enter the ports in the bottom of the piston and slam it down.
Once in a while I have had backfires immediately followed by a "clunk" that
I would bet was the piston slamming down, always with a cold engine (but not
THAT cold!).
--
George Downs, Bartlesville, Oklahoma, Central US