I have a ranch house built in the early 1970's in northern California. The air ducts are an open channel down the hallway with vents to each room. They are framed with wood and sheetrock. I want to replace this. Any suggestions?

You could use some good grade flex duct to replace it with. The flex is already insulated and sheet metal boots are made for round flex to attach to. I would buy the highest R rate flex. It may cost a bit more but you will have a lot less heat and A/C loss.