I spoke with the conversion company who federalized the car for me. They confirmed that the new owner must apply for approval from the NHTSA prior to the sale being completed if the car is sold in the USA. They are happy to help the new owner with this or the new owner can handle it themselves. The process takes 30 days on average, but can be expedited at a cost if need be.
Update: The car took the "Best Mercedes-Benz AMG" award this weekend at the annual Exklusiv show at the Mercedes Vehicle Preparation Center in Long Beach.
Thanks for the kind words guys. Ed - The car is U.S. titled and would incur VAT charge if returned to Europe.