There really aren't any 'cons' to switching from factory irons to aluminum heads. Factory big-block heads need quality (=expensive) work to get them even close to the out-of-the-box performance of the aftermarket stuff. Much better flow, less weight, modern chamber....no-brainer if you have the cash. If there's any drawback at all I guess it could be that you really need to verify the guide clearances, valves seats/job, and spring setup is right before running them, although plenty of folks just bolt them on and go but that's too big a gamble to take IMO. If you're not set up to do it yourself, most shops don't charge much just to measure and verify. Angled plugs are usually a big help with headers.