No matter what "dispensation" you refer to, there is just one Christian faith. Galatians 3:21-29 (WEB):
(21) Is the law then against the promises of God? Certainly not! For if there had been a law given which could make alive, most certainly righteousness would have been of the law.
(22) But the Scripture imprisoned all things under sin, that the promise by faith in Jesus Christ might be given to those who believe.
(23) But before faith came, we were kept in custody under the law, confined for the faith which should afterwards be revealed.
(24) So that the law has become our tutor to bring us to Christ, that we might be justified by faith.
(25) But now that faith has come, we are no longer under a tutor.
(26) For you are all children of God, through faith in Christ Jesus.
(27) For as many of you as were baptized into Christ have put on Christ.
(28) There is neither Jew nor Greek, there is neither slave nor free man, there is neither male nor female; for you are all one in Christ Jesus.
(29) If you are Christ’s, then you are Abraham’s offspring and heirs according to promise.
It doesn't matter whether you believed in Jesus before or after Paul started his teaching, if you believed then you are a member of the one "body of Christ". 1 Corinthians 11:3 (WEB):
(3) But I would have you know that the head of every man is Christ, and the head of the woman is man, and the head of Christ is God.
Ephesians 4:11-16 (WEB):
(11) He gave some to be apostles; and some, prophets; and some, evangelists; and some, shepherds and teachers;
(12) for the perfecting of the saints, to the work of serving, to the building up of the body of Christ;
(13) until we all attain to the unity of the faith, and of the knowledge of the Son of God, to a full grown man, to the measure of the stature of the fullness of Christ;
(14) that we may no longer be children, tossed back and forth and carried about with every wind of doctrine, by the trickery of men, in craftiness, after the wiles of error;
(15) but speaking truth in love, we may grow up in all things into him, who is the head, Christ;
(16) from whom all the body, being fitted and knit together through that which every joint supplies, according to the working in measure of each individual part, makes the body increase to the building up of itself in love.
Jesus is the head of the Church, and there is only one Church. The Hebrews were/are a part of the Church. Paul said they were - Hebrews 3:1 (WEB):
(1) Therefore, holy brothers, partakers of a heavenly calling, consider the Apostle and High Priest of our confession, Jesus;
Paul taught about the blood of Christ in 1 Corinthians, Ephesians and Romans. 1 Corinthians was written in around 53-57 AD, Romans was written in around 57-58 AD, Ephesians in around 60-64 AD. Hebrews was written between 64 and 70 AD. Therefore there is no reason to think that the Hebrews were not part of "our church" or that they believed differently to the non-Hebrew members of the Church.