Got any pictures? Removing ceiling joists has an ominous ring to it. Do you believe they were added just for excess (overkill) or do they look like they NEED to be there? Tough call w/ out a picture, but I'd be leery. People don't often put a bunch of wood in a ceiling just for kicks and giggles. Are the 2x4s the bottom cord of a truss? A 16' span is a long-butt way for a 2x4 to go all by itself; way, way long.