A quick answer to all your questions is that Pontiac engines are as different from Chevy's as Ford's are to Chevy's. Very few parts are interchangable (maybe carbs, distributor caps, a couple of thing like that). An easy way to tell the difference is the Pontiac engine has an aluminum timing cover/water pump assembly with the fuel pump bolted to in on the right side (looking at the engine). The Chevy has a stamped steel timing cover with a water pump that sticks out away from the motor and the fuel pump is bolted to the left side (looking at the motor) of the block.
