Looks like a perfectly ordinary cheap derailleur to me; I can't imagine Huffy would use anything else. Just go to your favorite Walmart and pick up one of the replacement cable sets they sell there. You should get two derailleur cables and two brake cables for about 5 bucks.
The hardest thing to do will be to cut the section of housing (the part that the cable itself slides through) to the proper length. The shifters on this old bike are probably friction-type; the cable just threads through a hole in the shifter arm.