Piston ID

Compression height is the distance from the middle of the wrist pin to the top of the flat part of the piston.

340 from 68-71 stock compression height with a 3.31 stock crank is about 1.81”
360 stock compression height with its 3.58 stroke crank is about 1.67”.

Measure the flat part of the piston to the top of the wrist pin bore and add 1/2 of the wrist pin diameter or (0.984/2 = 0.492”) to the above measurement.

This should give you an indication which stoke crankshaft the piston is for.