if a turbo has an internal wg there's nothing stopping you from welding the wg shut and going external....or using a bracket to hold it shut and going external....just like most turbos have to do at the moment....vice the large turbos that only come with ext wg turbine housings
for the twin scroll applications they are offering the internals to save $$ and space
"EFR optional internal wastegates are aerodynamically-optimized to offer the same performance as an external wastegate recirculated back into the downpipe - no 90 degree corners here. This is a real "value" feature of the EFR program, particularly in the case of twinscroll applications which require (2) external wastegates, (2) manifold wastegate ports (2) dumptubes for maximum performance. Furthermore, the manifold fabrication and installation are both simplified with the wastegated EFR models. Boost levels can be easily adjusted by swapping adjustable wastegate canisters available in three different spring rates/boost levels. Lastly, different turbo clocking positions are easy to accomodate without changing the wastegate bracket. This is because the bracket is bolted to the bearing housing backing plate - not to the compressor housing as is the case with most internal WG turbos. For space constrained applications which can not fit the EFR internal WG or Hardcore racers that want to keep their dual external wastegates mounted to the exhaust manifold - you can do that too!"