An AFC would help if you're running rich up top, since you can use it to lean things out as necessary. If you're running lean, don't expect to be able to do that much with an AFC, since you'll throw a MAP sensor code if you try to add more than a 10-12% value or so. All of this should be dyno tuned, of course, preferably with a wideband O2 for A/F readout.