340 marine engines.

Marine:
Built for higher rpm usage than industrial motors, they regularly see extended use at higher rpm.
Dual engines had one running in reverse rotation. The reverse rotation engines used different starters, cranks, cams, oil pumps, distributors, and crankshafts; none of which are useable in a passenger car. If you have a RR engine, it's basically good for the block and heads, and a few small parts.