The bike is a Manco based off what they called a scamp ( a name and I think design they picked up from Fox corporation after they went under), they were also sold through Sears at the same time. I have never seen one outfitted like yours but that tank is a Manco used one as well of the same era. I do kinda think it was converted though, the tank straps look welded after the paint, and the engine head bolts have the 2 long studs with spacers to hold the orginal tank on the engine....just stuck on the back two head bolts. the bike should be right around 1977/78 The engines head design and head bolts kinda say that as well.