I have at my disposal a set of stock 5.3 heads. I have a camaro with stock heads and an ms3 cam. I know I would have to change the cam out to run these heads but my question is, with a stock to mild cam would I be able to use the un ported 5.3 heads and what kind of power gain or loss am I looking at? also I am using a ls1 intake manifold but may go to an ls6 soon.

Not worth it if they are stock 5.3s. The valves are smaller and you will only choke up your motor.