I talked to him a few years ago at a car show. IIRC, he has the engine rebuilt every 400,000 to 500,000 miles. The car itself is very simple. 1 belt turning the alternator and water pump. No other accessories on the engine. Manual brakes. Manual steering. No A/C. The car has been repaired and repainted several times.
As far as the most miles on an original engine, I remember a guy in North or South Carolina that had over 1 million miles on his small block Chevy pickup. His job was delivering something printed (newspaper?) every day to Georgia. His round trip length was over 700 miles a day. He had his oil changed every 4 days at a Pennzoil quick lube shop where he lived. After he hit 1 million, Chevy gave him a new pickup in exchange for his old one.