I found a parts boat with a 340 in it and was wondering if it's worth buying to use the engine in a car. I know most of the 440 engines in boats rotate in the oposite direction, but is that just a matter of replacing the crank?

Well yes and no... the crank is less of a problem than the cam and gears..they have to be changed to a standard rotation ( car ) cam and gears..the crank can be used if you have a machine shop grind ( polish )off the nearling by the rear seal..another problem is if it was used in salt water..A serious corrosion problem there..And not all marine engines turn reverse...A stern drive motor is the same rotation as a car.. only single engine inboard and the right motor in a twin engine inboard powered boat. rotate reverse rotation .A lot of the mopar engines were used by Volvo penta and were used with stern drives and are standard rotation,,even the twin engine boats with stern drives are both standard rotation

Thanks,
I'm not a boat person so bear with me. If the motor is not running, how can I tell if it is car rotation or otherwise?

If it has been in salt-water without a heat-exchanger,just pass on it.If a heat exchanger was used it might justify further investigation.

My buddies open bow Chapparal had a GM305 stern drive, regular clockwise rotation.

The 340 boats that we sold that were made by Chrysler Boats had regular clockwise rotation. Make sure of what you have before jumping to conclusions. The boaats I am referring to were produced in the mid 70's.

is the boat savable? i would buy it and restore it sure an unusual one dan

As I said ..stern drive boats are standard rotation