People get hung up on timing issues. God is eternal, Jesus is the atoning sacrifice for the sins of the whole world, not just from that point on. Whether or not you can call a person who lived before Jesus a "Christian" is simply splitting hairs that are irrelevant.
Whenever there is doubt I remember this verse:
Matthew 19:26
"Jesus looked at them and said, 'With man this is impossible, but with God all things are possible.'"
I'm not fighting if the person before Jesus was a Christian or not.
Christian is a term that equals redeemed of Christ, redeemed of God.
I'm actually not arguing anything.
I did offer, through scripture that without the shedding of blood there is no remission of sin.
I also offered, through scripture, Abraham believed God and it was imputed to him as righteousness, no blood was shed at the time.
Abraham is a Jew, by birth, he is a Christian by second birth, simply by believing God.
Scripture tells me, you must be born again, Scripture deals with the second birth.
I haven't read all you have posted, I doubt we disagree.
To make my stance clear,
Jesus is eternal God, in flesh, when Abraham believed God he was imputed righteousness by trusting God, at that point, the actual payment for sin would come later.
In my mind this is nothing to argue about.
Just let the redeemed of the Lord say so.
I've been bought, I'm redeemed.