the divider better be very tight precision fitting to not allow any exhaust to leak between the wastegate port and turbine port on the turbine housing. i bet any small amount will cause turbulence. i think an easier (and better) maybe even cheaper solution if you want external wastegates would be to just drill a hole in your exhaust manifold and weld on a pipe for the wastegate.
--.scubasteve.--
(Rebuild started: April 2004. estimated completion: sigh)