Definitely a Murray built “space frame” but not a Sears. Sears bikes, Flightliners / Spaceliners will have MOS 502 stamped on the left rear dropout; which is Murrays code for Bikes they built for Sears. What ever it is, it’s missing the tank. Otherwise it wouldn’t have the bracket on the back side of the end tube. Google ‘Murray Serial Number Project’ for the thread here on the CABE that coluld give you some clues as to which retailer this was built for. Gambles sold Hiawatha, OTASCO sold Flying O, Pennys sold Foremost. Sears sold JC Higgins or Sears (depending on the year), etc. All built by Murray of Ohio.