I don't see the gospels as integrated. Yet you use the word "different". They are not the same. For instance Abraham's gospel is;
Gal_3:8 And the scripture, foreseeing that God would justify the heathen through faith, preached before the gospel unto Abraham, saying, In thee shall all nations be blessed.
You say Abraham's gospel is an "early rendition of Paul's gospel. Please compare them both.
Abraham's gospel; In thee shall all nations be blessed".
Paul's gospel;
1Co 15:3 For I delivered unto you first of all that which I also received, how that Christ died for our sins according to the scriptures;
1Co 15:4 And that he was buried, and that he rose again the third day according to the scriptures:
Do you think they look alike ?
They are different. Paul's gospel was distinct, not known before by men.
Eph 3:4 Whereby, when ye read, ye may understand my knowledge in the mystery of Christ)
Eph 3:5 Which in other ages was not made known unto the sons of men, as it is now revealed unto his holy apostles and prophets by the Spirit;
Eph 3:6 That the Gentiles should be fellowheirs, and of the same body, and partakers of his promise in Christ by the gospel:
We are not those people whom Paul was writing about. We are Gentiles and Paul is the apostle to the Gentiles.
For you to be saved as a Gentile you need to believe the gospel given to Paul by Christ.
Gal 1:11 But I certify you, brethren, that the gospel which was preached of me is not after man.
Gal 1:12 For I neither received it of man, neither was I taught it, but by the revelation of Jesus Christ.
This is what I have believed, the gospel given to Paul by Christ. If you add, subtract from it, then you have believed in vain as Paul writes.
1Co 15:2 By which also ye are saved, if ye keep in memory what I preached unto you, unless ye have believed in vain.
This is not my opinion, It is what God has written through our apostle Paul.
1Co_14:37 If any man think himself to be a prophet, or spiritual, let him acknowledge that the things that I write unto you are the commandments of the Lord.