Here's why I say the OT saints were born again...
James 2:23 said Abraham was God's friend. Now, the unregenerate, those devoid of God's Spirit, are His enemies. Romans 8 7-8 attests to that. Those in the flesh, those w/o the Spirit, are His enemies, at enmity with Him. Those in the Spirit, are those who have His Spirit, are born again. They are the only ones who can please God. So, to be God's friend, Abraham had to have God's Spirit within him.