With this question someone is going to give the answer that you are saved in the Old Testament by looking to the Cross, and in the New Testament by looking back to the Cross. That is not true. In the Old Testament they were looking for a Kingdom not a cross. There was no second birth or spiritual circumcision. A better word word for salvation in the Old Testament would probably be "safe" instead of saved as we think of it. The reason being that no one went to Heaven. Not one person who died went to Heaven. They were all in the center of the earth at a place called paradise or Abraham's bosom. When did they get out of there? When they believed on Jesus Christ. Jesus descended into the heart of the earth to lead captivity captive at the time of His death (This is just one thing that He accomplished while there). Jesus preached to them the Gospel(I Peter 4:6), which is the death, burial, and resurrection.
So, how was a person safe in the Old Testament? Well that depends on what time period you are speaking of. The most commonly thought of is the period of the Law. How was someone safe during this time? The answer is that He belonged to the nation of Israel. What you must understand is that in the dispensation of the Law, eternal security did not belong to an individual, it belonged to a nation. I will even take that a step farther and say that it was possible to step outside those bounds. Several times in Exodus through Deuteronomy, the Bible says a man can be cut off from the nation, thus ending in "loss of salvation."
Fast forwarding to the New Testament though, salvation and eternal security belongs to the individual. Just be clear on this fact, works has nothing to do with salvation in the New Testament. Salvation is by grace though faith. That includes getting saved and staying saved. Just a side note: Faith is only mentioned twice in the Old Testament, as compared to over 200 times in the New.

this is a further question and comment, rather than a solution.

what does Acts 17:30 play into this? when is the "times of ignorance"?
Acts 17:30 - "And the times of this ignorance God winked at; but now commandeth all men every where to repent:"

Was there anything about rule by conscience?

If during the time of Law, Israel could be saved and anyone who joined with Israel and kept the commandments, what about other nations? surely not everyone knew of Israel or their laws. were they then judged by conscience?

God "winking" can at the very least be taken to mean that he doesnt use the same measure as punishing rejection of Jesus (which would be damnation.) What exactly is "winking" though, according to context and comparing scripture with scripture?

The name of Jesus had not been revealed yet because they were in the dispensation of the Law. We are in the dispensation of Grace. Those are two different plans of Salvation. In the Law the Hebrews did rituals for the forgiveness of sins. But now under grace, we have Jesus, our high priest and perfect Sacrifce.
The psalmist is speaking prophetically of the incarnation. Notice verse one says: "the prophecy". God had not been manifested in flesh YET for our Salvation. Jesus is THE God Almighty manifest in the flesh. "What is His name and the name of his Son?" The bible is telling us that the Father has a name, and the Son have a name. This name is JESUS, the only name under heaven given to us for Salvation. Compare this verse to John 3:13.