340 vs 360

how do you tell if they are 360 or 340 pistons?

A the distance from the center of the pin to the top of the piston (piston height) on a 340 will be approximately 1.84". The distance on a 360 will be approximately 1.67". This measurement is to the flat surface on the edges of a dished piston and does not include the dome on a domed piston.