Ok

Here it goes, 351 is smaller lighter and easier to work on than the 428. The 428 produces more Hp stock than 351 but, 351 has cheaper performance parts in most cases cause it's more popular.

Positraction is exzactly what it says, it provides positive traction to both rear tires without any slip. Have ya ever seen someone light the tires on somtin like a ford ranger and only one tire lights, this is an example of a car without posi. When a car with Positive traction lights it's tires, both tires light up.

For u NOS is the Go Baby Go button that was pushed in The Shelby Mustang in " Gone In 60 Seconds ". It makes the car produce more hp and gain rpm's in return. Pros are the gained speed from the happy button but the cons are, NOS kits are expenisive and the bottles are shipped empty and the bottles run out of juice fairly quick.