You can have a sleeve welded in place but most replace with a new system, the Cobra Sport we offer makes a great replacement - http://cougarstore.co.uk/index.php?main_page=index&cPath=1_10
Which wheels are you getting and what's the spec, this will help us to determine which tyres are needed, usually 19" wheels have 245/35/19 front and 275/35/19 rears...
Scorpion only has one sound option, so you don't have to decide between resonated and none resonated, and it's louder than the Milltek but not to the point where it's intrusive...