This may sound too simple but is your throttle opening up all the way? When I first dynoed my mild 302 it only pulled 160 rwhp. Guys at the shop said that was about right.
I searched the Internet and a poster at ford muscle said to check the throttle opening. I did and it was only opening up about 1/3. I adjusted it, took it back and it pulled a little over 280 RWHP.