Maybe I am confused.
1 Cor 15:50 Now this I say, brethren, that flesh and blood cannot inherit the kingdom of God;
The verse is often taken out of context. They cannot "inherit" the kingdom of God. But someday we will enter the kingdom of God.
Is to inherit salvation the same as inheriting the kingdom of God and inheriting eternal life?
No, I was given eternal life the day I was saved. It is the gift of God.
See Romans 6:23: The wages of sin is death, but the gift of God is eternal life. I may die some day physically; but I will never die spiritually for I have eternal life.
--Depending on your view of eschatology, if the kingdom of God is the Millennial Kingdom, yes some day I will inherit that. I will gain entrance because I am saved; because I already have eternal life. The same is true for Abraham. Righteousness was imputed unto him (Rom.4:3).
Does the great salvation of Heb. 2 that we are not to neglect which Christ first began to preach have anything to the world to come see verse 5. Is that the kingdom of God?
No, that is salvation through Christ, by faith.
Just what world do you think Paul believed Abraham is heir to in Romans 4?
The same salvation that we have.
For the promise, that he should be the heir of the world, was not to Abraham, or to his seed, through the law, but through the righteousness of faith. (Romans 4:13)
And therefore it was imputed to him for righteousness. (Romans 4:22)
Will Abraham be in the kingdom of God? Luke 13
There is no reason to believe otherwise.
Is this the same kingdom of God one has to be born into in order to enter?
Jesus said to Nicodemus, a ruler of the Jews, one who was looking for the Kingdom to come at any time:
Jesus answered and said unto him, Verily, verily, I say unto thee, Except a man be born again, he cannot see the kingdom of God. (John 3:3)
--Taken in the historical context I believe it is.
And if ye [be] Christ's, then are ye Abraham's seed, and heirs according to the promise.
Just what do you thing these Jews and Greeks who become Abraham's seed through Christ inherit?
Those who are Abraham's seed are believers in Christ. They inherit eternal life.
We are heirs of the hope of eternal life in the kingdom of God. The gift of God.
One comes before the other. One cannot have entrance into the kingdom of God without first having eternal life, the gift of God which comes at salvation.
For as the Father hath life in himself; so hath he given to the Son to have life in himself;
Abraham does not have that yet nor anyone else other than Jesus the Christ.
What you have is Christ in you the hope of glory.
If I have Christ, I have eternal life:
The thief cometh not, but for to steal, and to kill, and to destroy: I am come that they might have life, and that they might have it more abundantly. (John 10:10)