340 marine engines.

Do NOT use a reverse rotation crank in a car application- it will run fine, but the "knurling" on the rear main seal journal is in the opposite direction. Intended to help move oil away from the seal and prevent leaks, a RR crank run in standard rotation will actually force oil OUT past the seal.
If I remember correctly, a reverse rotation engine will have "RR" stamped on the front of the block below the left cylinder head along with the rest of the engine info.