I've run a '77 f-150 w/460/auto [300,000 km]and a Chev 1-ton van w/350/auto [570,000 km] on strictly propane. It was fine for what I needed. It always started, even at -35C. At -42C the liquid will no longer turn to vapor but I'm sure a battery blanket on the vaporizer would cure that. My research tells me that it's not economical to convert to propane until the price of gas is 2x the price of propane. If/when I was/am rebuilding a carb engine and had/have a local source of propane I would/will build the engine for propane @ ~ 13-1 compression ratio [I need to do more research on this, I want to run the highest compression ratio feasible], as propane has a very high octane rating I could then have my rumpity-rump cam in a street driven hot rod and not have to pay through the nose to run it. This conversion makes a lot of 'cents' when you start pricing racing fuel. Another benefit for 4x4ing is that the motor will run at any angle... no float bowls to screw up, but you should also run a kill switch for the same reason.
I have not researched efi set ups too much but I know they are out there, check the link in my previous post.
This is not a do-it-yourself project unless you are very knowledgeable about the different systems involved, and you may need an inspection... in Canada you will. This is not to say you can't learn what you need to know, that's the route I'm taking.
Richard