sorry 64 dartwagon, but you cannot run a single flare for non high pressure lines, a flared line is a flared line. it just depends on SS or regular steel. it is ok to have single flared SS brake lines since it has no seam and wont split.
Single flares have been used in non-high pressure for years. In saying this I am referring to other things not just brake lines. As I treat a brake system as a life saving device. And I would suggest practicing outside the car on a piece or two before going under, the biggest help for double flaring is to completely remove the bur from the tube cutter. And I use brake fluid as a lube for the inverting button so it doesn't hang up and break the button.