I wanted to buy a pair of Shorty Headers for sound for now and maybe later go to long tubes, and i didn't know if they could be bolted on to the existing stock pipes or do the Shoties need welding also ?

 

Shorties are theoretically supposed to line up with the stock Y pipe location. Whether that is always the case or not I can't say, but I've heard of some not lining up correctly. I would recommend saving up for long tubes.