this is a March 53 Schwinn welterweight.arch bar frame with heavy duty S4 wheels,3 speed sturmey archer rear.the bars had been swapped out along the line,but have been corrected since the pics.
these were only offered in the 53/54 catalogs,but i've never seen a 54.touted as a delivery/heavy duty lightweight,these are pretty hard to find in any condition.luckily,this one is super nice.
pretty sure the 7 is a month stamp,but the frame is a March serial number.usually the case as the frame serial doesn't represent the actual build date.