It certainly resembles a tool used to compress tappet springs in a diesel fuel injection pump. The slotted part would connect to a bolt on the pump bottom, the pivoted piece would force the tappet against the spring (as you push on the handle) and you would insert a pin to hold the tappet in position. With the tappets "up" the pump camshaft can be moved into place.
Like I said it closely resembles such a tool - not sure if that's what we have here. Al.