The 8200 head I just purchased does not cut as clean as I would like. Leaves more stems sticking up than I would like as you look back across the field. I have adjusted the head so it is cutting as low as possible. It has the SCH knifes and with the SCH PRO Drive. Sickle and guards are in fair shape. Currently have a drive pulley of about 7.75". Can you put a bigger drive pulley on this head and it so what would be the part number.