Lift is decifered in the camshaft not heads. Valves will lift until they hit something or the valve springs reach coil bind. Is that what you were asking? Maybe I missinterpreted your question..
Your heads aren't the limiting factor. You need to talk to an experienced and reputable engine builder about matching your intake/cam/heads in order to get the best package. If these components aren't pretty well matched you'll be pouring a lot of money into something that won't run very well. You need to spend the time to develop a plan.
Other possibilites are: Finding a good crate motor that makes the hp you're looking for; or I think Edelbrock and maybe some others market intake/cam/head packages that are matched. You just buy as much hp as you want/can afford.
a custom grind cam (flowtech induction, camshaft innovations) will probably be your best bet. if not a custom grind call comp for a cam recommendation. i would definetly go with afr 165's if you are going to spend the money on aluminum heads.
there are plenty of people in the 95 5.0 section that easily make 300 at the wheels with the afr heads ,upgraded intake and cams. go to their website and see what they did to a 95 gt http://www.airflowresearch.com/95mustang_dyno.php. flowtech induction/cammshaft innovations will help you match all the components to get the most power possible. you won't be disappointed with afr's. i had them on my 357 and that motor was a real hoss! go to the 5.0 section and serach afr's also to see for yourself
jake