Actually, it is quite specifically supported by any number of scriptures. Three of the critical examples are the entire BOOK of Romans, which deals with the question "if the Gentiles are now the 'people of God' just by faith in Jesus, how does that affect all the promises of God to Jews down thru the years?" To summarize, Paul argues what I just said above in the previous post...., the message has ALWAYS been that of faith, and there has always been a "remnant" within Israel who were the TRUE people of God... those of the faith of Abraham.
The message of Galatians is essentially the same, with a little bit different twist.
Finally, Jesus is represented as explaining that the entire Old Testament was about HIM, both in his dealings with the "church leaders" of his day and in explaining that the OT scriptures were written "concerning himself." (cf Luke 24:27 And beginning with Moses and all the Prophets, he explained to them what was said in all the Scriptures concerning himself.)
There are many other passages, but these are representative of the central message that there IS one central message, about one central person, and faith in that person as the provision for redemption is the theme of the one book, comprised of many smaller "books."
Therefore, the OT Jews would have been "in heaven" when they died for the sme reason as a NT Jew (or Gentile) would be in heaven upon death., and that would have been contingent on faith in Jesus as he had been revealed as "coming" in the OT. That is the central message of the bible itself, and is echoed by every serious scholar from Athanasius, Clement (both of them), Gregory of Ny., Augustine, Cyprian, etc etc etc.
So, in other words, a jew is condemned to hell unless he violates the pieces of his orthodox teaching he holds to be fundamental: the shema and the 1st Commandment, by accepting christ as savior.