When using input from SYSIN, you are limited to 80 byte records and can specify only one DATACLAS with properties that can span multiple lines.
The following is an example of JCL that uses SMS DATACLAS with SYSIN.
//STEP20 EXEC PGM=MFCMD //SYSUT1 DD DUMMY //SYSIN DD * DATACLAS NAME(ABC) RECFM(FB) LRECL(80) FUNC(ISRT) //SYSUT2 DD DSN=TEST.OUTPUT,DISP=OLD //SYSPRINT DD SYSOUT=* //SYSOUT DD SYSOUT=*