A pull-type mower conditioner includes a crop harvesting header vertically movable relative to the frame of the mower conditioner between a raised transport position and a lowered operative position, a lift mechanism to effect the movement of the crop harvesting header relative to the frame, and a transport latch mechanism to control the locking of the lift mechanism in the transport position. The transport latch mechanism has a biasing lever operably positionable between locking and unlocking positions. An extension spring is connected to the biasing lever to bias the lever in the selectable positions. The transport latch will not engage whenever the header is moved to the transport position to avoid an obstacle unless the biasing lever is moved to the lock position. Once the biasing lever is adjusted to bias the transport latch into the lock position, the raising of the header into the transport position will actuate the transport latch and lock the lift mechanism from returning the header to the lowered position. The lift linkage incorporates a cam mechanism that serves as an upper flotation limit under normal operating conditions and automatically converts into a device for securing the header in the transport position when the header is moved into the transport position.