Small block intake

@BLIMP IMO, the best things you can do for extra power BEFORE you open up the engine would be...

1: A 4 bbl. carb, your choice in maker and style, but 600 cfm will be very good on the square bore carbs.
(Edelbrock or Holley)
A Thermoquad is my fav OE offering. Small primary/large secondary good for mileage and power.
Top it with a OE 4bbl. air cleaner.

2: The intake could be the OE iron (should be cheap) or the Edelbrock offerings. A Performer would be best IMO.

3: Use a MSD or similar spark ignition and recurve your distributor. Open up that spark plug gap!

4: Dual exhaust off of the exhaust manifolds with a H or X pipe will help it breath easier and increase power and mileage.