Turbo should onky cost at max 1250 for your current one to be high flowed and rebuilt. Jetwreck had mine done by Precision Turbo for a Sierra stage one. They can do a pretty much one day turn around. Alternativly you can send it down south to to hypergear who charge 850 for the service but have a 1-2 week turn around.
Jetwreck is the man for doing the change over also. These are one of those cars that if they haven't done it before don't take it to them.