When Eph. 4:8 talks about Jesus leading a host of captives, I don't think it is talking about people who died before Christs time, and I don't necessarily think that those he led captive are the same as those he gave gifts to. When he lead "captivity captive" I think it is referring to the demonic forces (and all that entails) and illustrates how he defeated them by all that he accomplished. I think when it talks about the giving of gifts, it is referring to men now being able to receive the spoils of his victory over those demonic forces that he defeated. But it says plainly that when He ascended He led captivity captive. It doesn't apply that saying -'led captivity captive', when He entered the belly of the earth(hell). Even if you take the meaning as figurative, where would the demonic host be? In heaven(ascending), or in hell(descending)? Also, when He ascended and led captivity captive, it says He 'gave gifts to men(and women); were are the fallen angels? Why was He busy giving gifts to mankind if He was escorting fallen angels to the abyss? Eph. 4:6 and Eph. 4:9,10 are two completely different actions taken by the Lord.
I agree with you when you say that Jesus was the first fruits of a righteous life...and I know that no one can come to the Father except through Jesus. I am not trying to say that there is, or was, another way to heaven (or God) - I believe that God's plan for redemption was clear, even in the OT - and that the OT points us to Jesus. I think it is possible (I can't say for definite because I wasn't alive back then...) that righteous men from those times would have still been able to put their faith in Christ even though he hadn't walked the earth yet.Yes, it is a written fact that they did. I think that they still would have known that God would send the Redeemer as a sacrifice. That's how David could record messianic prophecy in the Psalms, and how Isaiah could understand the meaning of Isaiah 9:6. God had been revealing his plan ever since Adam and Eve sinned. So, I think it is possible that OT peoples were able to put their faith in Jesus without his actual human birth happening. Yes, they did, that is infact what happened. But they were not yet able to enter into the kingdom of heaven. (So the place called Abraham's bosom was their residing place.) These are the souls Jesus led into heaven, giving them gifts for their obedience.