I can't imagine the stock fan is too effective without the shroud since it sits so far from the rad. The idea of notching the stock shroud and filling it with fiberglass or plastic crossed my mind, but i never checked if theres even enough clearance between the fan and the shroud to do that.
My plan is dual 12" fans for clearance and safety. Looking in the engine bay, i'm not sure a centered 16" would fit because of the stock fan "spindle". However with duals, it allows that spindle to sit between the motors, as well as leaving space at the top of the rad for a charge pipe, and as already mentioned, will still give some cooling if one quits. My only worry is the load on the charging system.
I replaced my alternator with a lifetime warranty rebuilt one last year, and voltage still dips below 12 volts (on the factory voltmeter) when its cold out and blower, wipers, headlights and amp/stereo are going.
I've heard mention of using bigger gm alternators on this site, but never saw whats involved.