GE does a few. NS has the Dash9 rebuild program that results in a DC to AC conversation called the AC44C6M. Some are being rebuilt by NS at Roanoke and Altoona while NS has contracted with GE to produce others. I don't know about any other road's rebuilds. NS also has the Dash8.5 rebuild which, I think, was mostly being done by GE, but that program has stalled. There might be technical issues. It's just a rebuild, not a DC-AC conversion.
NS also has the SD90MAC to SD70ACU rebuilds. Most are being done at Altoona, but EMD/Progress has a few. But they may be busy as NS recalled 4 units sent to EMD so they could rebuild them at Altoona.