Nice looking car and photos. Nice to see that they've improved the road.
Think about looking for a used 12v motorcycle plug-in coveralls type thing. Good ones keep you toasty well below 20 degrees F.
If you have a tonneau cover, get the heater on max and it'll fill the covered side of the cockpit with enough coming out from under to help you out a lot. At the least your right side and arm will be good.
I saw a guy in a Triumph TR4 with a hood sewn onto his tonneau cover. It was OD color so maybe he cut it off an old M65 field jacket or something surplus. He was on the freeway south of Portland, OR driving along at 60+ mph in the rain with the cover all buttoned down and his hooded noggin sticking out. The crazy sucker was smiling and waving at the people in cars as they passed by.
Thing is, where there's a will there's a way, right?