The first thing to point out is that Tony assumes that the definition and the parameters of "the gospel" are beyond dispute. According to Tony, the gospel is embodied in a series of propositional statements that one affirms in order to become a Christian. Reading through the gospels, that simply isn't what I read in the teachings of Jesus. Quite possibly it seems that evangelicals of Tony's ilk agree, since tracts that are meant to represent the gospel such as "Two Ways to Live" choose not to incorporate any of Jesus' own words into their gospel presentation. Apparently, the Jesus of the Bible and the Jesus of history is much too inconvenient for the evangelical understanding of the gospel.
Given that evangelicals don't like to refer to Jesus when they talk about the gospel, it's not the least bit surprising that their understanding of the gospel has become somewhat warped, as evidenced in what they call Penal Substitutionary Atonement. I think more than anything else, this explains why evangelicals have consistently failed to construct a coherent framework to adequately understand the interrelationship between what they call the gospel and good works. Interestingly, it is worth mentioning that James deals at length with the problem of a faith that does not express itself through works and works that exist independently from faith.
I'd suggest that if evangelicals were to take the teachings of Jesus seriously, then they wouldn't have the problem that I've discussed above. The first thing to point out is that Jesus places considerable focus on what he identifies as the "Kingdom of God". It is clear that while the Kingdom of God involves an eternal element, it is also a presently unfolding reality. Several times in Scripture, both in the teachings of Jesus and elsewhere, the Kingdom of God is contrasted to "this present evil age", which is construed as nothing less than an opposing force to the Kingdom of God that Jesus is establishing. The establishment of the Kingdom of God involves tearing down the strongholds that hold humanity captive - and we see this in the ministry of Jesus in his determination to strike against the purity, debt and social codes of his days. His words in Luke 4:18-19 are particularly poignant:
The Spirit of the Lord is on me,
because he has anointed me
to preach good news to the poor.
He has sent me to proclaim freedom for the prisoners
and recovery of sight for the blind,
to release the oppressed,
to proclaim the year of the Lord's favor.
There is one important last word to say on the subject. Social justice is not the sum total of the gospel. Jesus' ambition to bring about a reconstituted humanity is not completed by building a well, or alleviating hunger - it is only started. Jesus' vision of God's Kingdom coming, when "His will be done on earth as it is in heaven" involves a complete reappraisal of values, both individually and corporately. The first step is freeing the captives. The second step is maintaining this freedom - and this will only occur when people are under the jurisdiction of Christ.