My 84 T is pretty much stock except for a Joe Lubrant chip, hotwired 340 pump, cold air kit and a 237 regulator. I can get away with 17psi 0 knock on 91pump gas. If I go up to 18, it knocks above 6degrees. I consider mine pretty stock because you should install a new fuel pump and hotwire it anyway.
Get a boost gage and scan tool and you can find out how much boost is safe.