The 60-Day Guide also references the Official Guide for Quantitative Review, 2nd Edition (https://www.amazon.com/dp/0470449764/ref=cm_sw_su_dp) and the Official Guide for Verbal Review, 2nd Edition (https://www.amazon.com/dp/0470449756/ref=cm_sw_su_dp), so you might consider using these resources.
Also, unless you still remember all of the question in the Official Guide (OG), you can probably still answer these questions a second time.

Finally, if you follow the 60-Day Guide, you'll need either the GMAT Prep Now video course or the MGMAT books. Both of these resources have hundreds of practice questions to supplement the questions in the various official guides.

I hope that helps.

Cheers,
Brent