can i put this turbo on my rst
 

You could if you change the exhaust housing over.

yes, can be fitted,
downpipe need changin

any ideas what down pipe, and where from?will it be more laggy or not that bad?

im assuming your not going to run the restrictor???

Whats your spec, will be really laggy on most 1600's

You'll need a custom downpipe made to fit cossie housing