how to get power from a 318

Stick with the stock 318 head and port them or use the Magnum heads stock. The problem with the 302's is head cracking between the valves. I here lots-o-problems finding them without cracks.
Queery? Edelbrock doesn't make a 700. They have a 600 and 750, 800.
The performer and 600 are a good combo. The gear ratio is very low, so if a change isn't coming, a small cam is in order.
For a off the shelf cam, Comp Cams has the XE256H. I would recomend this because it will work with the gears and converter without problem while retaining excellent vaccum for brakes and anything else needing vaccum.