The first Q is. How much do you want to spend. You are not going to get big power from the A12 without throwing big cash at it. And big power = unreliability if not done properly.

Stick with the basics. A nice size cam, nothing massive, 32/35 weber, extractors and a 2 inch exhaust and after all that, if you still have any cash left over, then a mild port job. Polishing is rubbish for a street engine and too much porting can make it go backwards in the mid range where you want the power. Round port heads are fine for a mild street engine.

Do you plan to do alot of the work yourself?