Be glad to, but remember...you asked for it, lol
We are not saved by faith we are saved by grace through faith. That might seem like splitting hairs but the fact is that if we are saved by faith then we are saved by something...we do. Secondly, faith is the result of something, right? So where do we receive the knowledge of whatever it is that we place faith in? Simply put, faith has always followed revelation from God. Men and women must first hear God's will in order to believe, have faith, and obey. This is a consistent pattern throughout Scripture. Abraham is said to be declared righteous, that is, justified...after he was told he would have a son of his own loins and that son would be the source for blessing to all nations of the earth. He believed God would allow his presumably barren wife to bear that son. So the point would be this: saving faith can only be accomplished when it is expressed towards God in obedience to His will. It is by grace that God gives Man the revelation necessary for his salvation, no matter what Age/Era we are looking at.
Now, concerning the second part of your question, that there are different dispensations/administration is a Biblical fact (though some refuse to recognize this). No man was under the Covenant of Law prior to Moses, right? But they were from Moses to Christ. So we see two differing Ages and within those two Ages we see Revelation from God differs. Abraham, for example, received a veiled Gospel of Christ concerning his seed, but did not know He would be God manifest in the flesh come to die in his stead. Isaiah had a more detailed, though still veiled knowledge of the Christ as reported in Isaiah 53, yet neither did he know He would be God manifest in the flesh come to die in his stead. The very disciples of Christ walked with Christ and ministered under Him preaching the Gospel of the Kingdom, and in fact, the Father revealed to them that He, Jesus, was the Christ (that had been prophesied) and that He was the Son of the Living God (Matthew 16:13-17)...but rejected the Gospel of Christ (Matthew 16:20-23). So we see that Revelation was progressive. I just wanted to make that point before I go any further.
Now I will make one point that is incontrovertible: Eternal Salvation is only possible through the death of Christ. That is the heart of the Gospel of Christ, that He came that men might not perish...but have everlasting/eternal life. So if we are going to say that men had eternal life in the Old Testament...where did they get it? Not, as some suppose, because the Lord gave it to them prior to Christ dying. There is a mystical delusion touted as Biblical Doctrine that is taught by some that this is the case. If that is the case, then why does Hebrews teach...
Hebrews 11:13 King James Version (KJV)
13 These all died in faith, not having received the promises, but having seen them afar off, and were persuaded of them, and embraced them, and confessed that they were strangers and pilgrims on the earth.
What we can say about the Old Testament Saints is that they were Justified by faith, which most Protestants as well as the Catholics confuse with Eternal Redemption. But note the quote above and understand that the Promise of God was in fact Eternal Redemption. They died not receiving that promise as well numerous others. Hebrews 9-11 makes the point that "Perfection," that is, Completion in regards to Atonement did not take place under the Law. And just to give a few verses to example that...
Hebrews 10:1-4 King James Version (KJV)
1 For the law having a shadow of good things to come, and not the very image of the things, can never with those sacrifices which they offered year by year continually make the comers thereunto perfect.
2 For then would they not have ceased to be offered? because that the worshippers once purged should have had no more conscience of sins.
3 But in those sacrifices there is a remembrance again made of sins every year.
4 For it is not possible that the blood of bulls and of goats should take away sins.
Hebrews 10:10-14 King James Version (KJV)
10 By the which will we are sanctified through the offering of the body of Jesus Christ once for all.
11 And every priest standeth daily ministering and offering oftentimes the same sacrifices, which can never take away sins:
12 But this man, after he had offered one sacrifice for sins for ever, sat down on the right hand of God;
13 From henceforth expecting till his enemies be made his footstool.
14 For by one offering he hath perfected for ever them that are sanctified.
In vv.1-4 we see that the sacrifices of the Law could not make the comer thereunto (the worshiper) perfect/complete (in regards to remission of sin, which is why the offerings were made) because they could not take away sin or the need for further sacrifice. But the Sacrifice of Christ makes us perfect/complete in regards to remission of sins...for ever.
So while the Old Testament Saints were "saved" from an eternal perspective, meaning their eternal destinies were secured because they were justified during their lifetimes, we must not confuse nor equate that to the Redemptive Work of Christ and what that accomplished. And we must not forget that their faith and belief, and yes, their works...were a result of receiving revelation from God in which they could believe, have faith, and perform works (and in that order, lol).
So no, they did not have Eternal Salvation until Christ died in their stead, eternally redeemed them, and liberated them from Hades, the resting place of the dead faithful in past Ages.
I hope this wasn't too long a response, Mikey, and I appreciate the very considerate query.
God bless.