3. Use INREC to get 13 bytes in my sorted file and using only 13 bytes in STEP2(COBOL program).
Note that INREC will shorten the records before they are sorted, whereas OUTREC will shorten the records after they are sorted. The less bytes you sort, the better, so INREC is a better choice here than OUTREC.
Of course, the only way to know for sure which method performs betst in your specific situation would be to try all three methods and compare the "performance" indicators you're interested in.