1. Grab a starter valve (SV) from Impco. It runs of the E-convertor via a 1/4BSP brass or plastic nut from the primary side of the unit. They are 12v battery operated solenoid which pumps raw propane into the area under the carb during cranking. There is a brass fitting with a restrictor. Should cost about $US 20, and comes with instructions.Works a treat!
2. Another thing to ponder. I've never liked the standard Dodge-style ten by 2 3/4 inch air cleaner. It's got lots of area, but it has paper construction and I doubt its open design will prevent the formation of ice crystalls. A K&N filter won't freeze up. It really needs a cover if its stock.
3. I think the cold makes the diaphram pretty intollerant of cracking open. Perhaps the idle richness needs resetting. They are very easy to retune, but the shop doesn't often have a fridge that big to do a set-up while that cold! Grab the Impco manual, and follow the trouble shooting page.