By adding one aftermarket part at a time doesn't seem to net much power gain until new heads are installed. Good article....
http://www.mustangmonthly.com/howto/26825/

 

Hi Soaring,
That sounds like what I'm doing. After removing my intake manifold I found a bolt had been broken off in a head swap. The old owner told me about the head work but not the bolt. I tried to remove it but no luck. So I am now looking at new heads but I think new heads might be over my mechanical knowhow. They sure look nice!!! Do you have any idea on the cost of the heads?
Thanks, Walt

 

JEGs has them for $499.00 each, so you are looking at a thousand bucks. But, they come fully assembled, so all you have to do is bolt them on.

 

The small valves and ports on the 289/302 have always been a downfall. The cost of aluminum heads have dropped considerably in the last several years. There is no excuse for anyone building a new engine to get these if you want horsepower. You can do all you want to a small block ford(except NOS, it doesn't matter then)to gain power but when you put good heads on, it will really wakes her up.