If the merge collector on your headers is not divided, then there's no point going with a divided inlet turbine housing. Just go with an open inlet turbine housing.
Here's an example of a divided 930 manifold suitable for a divided inlet turbine housing. The idea is to isolate exhaust gas pulses from the left and right side of the motor all the way to the turbine wheel to maintain exhaust energy and maximize turbo response.
http://goingsuperfast.com/images/Porsche_930_header_NEW-5.JPG
No affiliation... Just showing an example
