Are you seriously going to take a drug that was developed to fight breast cancer to counteract moobs you have gainned as a result of finasteride?
That is insane.
If finasteride is giving you side effects like this (it was the same for me) then its not working in the way it should be,it may have improved your hair but its clearly not agreeing with something. Also from my experience the gyno thing doesnt stop,it continues to grow gradually.
Read the propecia documentation that comes with the tablets.It says that if you have side effects which persist that you should discontinue the drug.
Your call tho