I thought 3sgte injectors were side feed...anyways, the 4ag uses top feed injectors.

Most, if not all modern wideband controllers have a narrowband output. This output is for exactly the reason you are asking about - an o2 input for the stock ecu.

Like what was mentioned already, you should have had the block machined as well specifically for a metal headgasket. I wouldn't reuse a failed gasket - why chance it over $100?

Smallport FWD Intake Manifold