I have a 306 with flat top piston (speed pro hyper) with stock E7TE heads, besides the trick flow valve spring kit, I run the Ford racing E303 cam 220 duration on intake and exhaust and .498 lift on intake and exhaust. I got it because it was a popular cam for the 5.0 motor at the time, but now it seems like people go with a cam that doesn't have the same amount of lift and duration on the intake and exhaust. If not this cam then probably somewhere around these numbers with the stock heads. I have my engine apart and I'm thinking of switching the cam because of what I've read on these cams and go with a split pattern and I'm also changing the heads. But like I was saying from what I've heard with stock heads I wouldn't go much bigger imo. I hope this helps in some way.
