Your biggest costs will be import duties + VAT, so he should verify with his local "Zollamt" what they will be: I think they will total 27%. The only way around the duties is if the importer owns the car in the US for more than 6-months beforehand and doesn't sell within 1 year after import.
He will have one year to register the car in Germany (verify with the Strassenverkehrsamt). The biggest hurdle will be getting it to pass inspection by the tüv. He can ask and clarify in advance if it is a straightforward inspection by providing them with the Baumuster (Chassis + Engine code, eg 210.032). If it was approved for sale in Germany already, there should only be minor mods needed. On my '87 VW Golf I needed to switch to Euro headlights (because of the Streuscheibe (lens pattern), install Standlichte (like mini DRL's in the headlight), and stick reflectors on the tail end. Some refits are more costly. The inspection itself will cost maybe 200 EURO.
Once it has tüv approval, the rest is more or less like the DMV in DC.

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