Actually, the German DB 601/605/603 engines were inverted V-12s, so you were sort of right. But the real difference is yes, they had fuel injection, and the Merlins didn't till a little later. And yes, rolling inverted and pulling to dive was the usual solution to the nose-over fuel problem in early Hurricanes/Spitfires. Once you had the desired dive angle, you could roll wings-level to the direction you were going.