I would drop the DCB infromation from the JCL, SORT will provide that, then it is only in one place for maintenance.,
You can't insert contstants with a REFORMAT statement, If you leave that as it is and then use INREC OVERLAY=(col:,X,col:X) that should do it.
Alternatively you can take out the 5,1 and use INREC BUILD to insert blanks. With lots of data this will be slower that using the OVERLAY.