Cold weather starting 1939 9n ford tractor.

This tractor has been in my family since 1942. it was my grandfather's, then my dad's, and currently mine !! Over the years, I have replaced the flywheel ring gear, kept oil changed, cleaned out carb several times a year. Replaced plugs, dad put rings, cylinder sleeves, and bearings in 1971. He also put in a truck 2speed rear axle diode in the wireing to the coil, for full voltage only when cranking.this helped alot but It has been iffy cranking in extreme cold or in our hot summers. I've put bushings in the starter, turned the armature, replaced the brushes also. it would turn the engine over quickly, however I felt like something else was lacking. I replaced the battery in Nov 21, it hardly made a difference. I figured out the cables were smaller than what it should have for a 6 volt system, these had been replaced over the years, probably because of battery acid getting in the cables. Of course they bought whatever was the least expensive, always. this cable cost me about 6 dollars a foot not including the ends to make up.
It made a big difference.