The seat and sissybar look to be the original style Schwinn used on their Stingrays. Look underneath for the brand or for a Schwinn Approved and/or Stingray logo on the back edge, it should be there. If it is the Schwnn seat and with the original covering, you could have something worth more than you paid for the bike by a long shot. Closeups of the seat would help. The Monark looks to be late 60's or early 70's, and it wouldn't be like in their heyday 30-40 years before this one was made.
WE HAVE THE LARGEST ASSEMBLAGE OF SERIAL NUMBER AND MODEL. BICYCLE COMPANIES SUCH AS MURRAY AND MONARK-SILVER KING.
The fully dressed out balloon tire bike was breathing it's last breath about the time this one was made. Probably not much collectible value, but you have the Schwinn looking seat for a consolation prize. That will bring some okay cash for your trouble.,BD.