Opus 67 contains six pieces, so check which number you are working on.
I have a list that advises the grade level of pieces, but I couldn't upload it as it is an Excel document with an .xls extention which is not allowed.

The grade levels are as follows according to this list.
Op.67, No.1 - Grade 7
Op.67, No.2 - Grade 7
Op.67, No.3 - Grade 6
Op.67, No.4 - Grade 8
Op.67, No.5 - Grade 6
Op.67, No.6 - Grade 7
I hope this helps.
allthumbs