What, a THIRD Gospel? There is no internal evidence in Romans that supports such a thing. Constructing such a thing requires not exegesis but inferencing upon assumptions based on presuppositions. It reminds me of the Supreme Court claiming that something in the text of the Constitution based on "auras of penumbras"
If you want to discuss these things with STP you better get used to his assertions which are based on nothing but thin air!
That is his
modus operandi.
Having made this point would Paul have approved of some alternative "Jewish Gospel" partially based on the Law? The strong all-inclusive language he uses in Romans 3 precludes any deviation from the one message of Grace that he taught.
The "good news" or gospel which Paul preached to the Jews here is not based on the law:
"And straightway he preached Christ in the synagogues, that he is the Son of God...proving that this is the very Christ" (Acts 9:20,22).
The Jews who believed this gospel were saved when they were given life by being born of God:
"But these are written, that ye might believe that Jesus is the Christ, the Son of God; and that believing ye might have life through his name" (Jn.20:31).
"Whosoever believeth that Jesus is the Christ is born of God...For whatsoever is born of God overcometh the world: and this is the victory that overcometh the world, even our faith. Who is he that overcometh the world, but he that believeth that Jesus is the Son of God?" (1 Jn.5:1,4-5).
This news was certainly "good news" or gospel to the Jews and believing that "good news" brought salvation to all who believed it:
"For I am not ashamed of the gospel (good news) of Christ: for it is the power of God unto salvation to every one that believeth; to the Jew first, and also to the Greek" (Ro.1:16).
The "good news" of Christ which was first preached to the Jews is the fact that Jesus is the Christ, the Son of God, and that all those Jews who believed that gospel were saved.
So that instance of "good news" perfectly fits what is said at Romans 1:16 concerning the "good news" of Christ