I have a thought experiment of sorts on a critical…

I have a thought experiment of sorts on a critical point in Acts at the Council of Jerusalem. If you were there and wanted to argue from scripture that was available, how would you argue that Gentiles do not need to be circumcised? By this point it is very possible that what was written was only Matthew, Hebrews, James and both Thessalonians. Could that primary point be made from the OT and those 5 NT books? I am aware that after Peter spoke James gave additional directives that were pastoral on executing the first declaration but what about before?