There is a series of books called "The Gospel according to Old Testament", going through some of the narratives in the OT and show how they are related to Christ. Perhaps those will be helpful when you are going through the OT with unbeliever, while keeping an eye on Christ the whole time.

Here is a link to wtsbooks:

Westminster Bookstore - Reformed Books - Low Prices - Flat Fee UPS Shipping - Gospel Acc. to the OT

Blessings,

__________________
Polo
Layman, Chinese Evangelical Church/Independent
San Diego

For from him and through him and to him are all things. To him be glory forever. (Romans 11:36)