You don't need to set anything in the ARCHPROC JCL regarding the parameter TRACKS. Just let is as below:
//ARPROC PROC SSID=,
//ARCHPROC EXEC PGM=OI,
// PARM='ARCHNTRK &SSID,&LOGNAME,&TRACK'
When OPS triggers an archive it will pass the estimated size in tracks of the OPSLOG archive dataset. For example, at the time OPS starts automatically this procedure you will see something like below:
//STARTING EXEC ARCHPROC,SSID=OPSS,LOGNAME='OPSLOG',TRACK=(500,500)