I would suggest not selling those headers. You can modify them to run an external wastegate setup for not much. Bill @ DSG did all the fabrication to set up a Tial MVS ewg with dump tube and relocate the O2 sensor bung. These headers were bulletproof (never cracked once with my launch control) and they sound amazing. I'm sure you know all this already, so just mod them instead.
Here is a link with pictures of the setup I had from when I sold it.