A header comprising a sickle drive (62A, 62B) for a plant cutting machine having a first sickle knife assembly supported for side to side reciprocating movement along a forward end of the machine, and a rotary power input for driving the sickle knife assembly, the sickle drive (62A, 62B) being disposed below a generally flat cover or floor having a forward end and bounding and defining an upper region of a generally flat cavity rearwardly of the forward end, the sickle drive (62A, 62B) including a rotatable first input element supported in the cavity for rotation about a generally upstanding first rotational axis by the rotary power input, a first eccentric element connected to the first input element for rotation therewith around the rotational axis, a first drive arm having a first end and a second end opposite the first end, the first end being connected to the first eccentric element for rotation about a generally upstanding first eccentric axis of the first eccentric element, the first eccentric axis being laterally offset relative to the first rotational axis for rotation thereabout, the first drive arm extending in a first direction from the first end to the second end, the second end pivotally connecting eccentrically to a first pivot element supported for rotation about a generally upstanding first pivotal axis, such that the first pivot element will be pivoted about the first pivotal axis by the rotation of the first input element about the first rotational axis, and the first pivot element being configured for connection to the first sickle knife assembly, such that the first sickle knife assembly will be reciprocatingly moved relative to the drive (62A, 62B) by the pivoting of the element the sickle drive (62A, 62B) further including a rotatable second input element supported in the cavity adjacent to the first input element for rotation about a generally upstanding second rotational axis by the rotary power input, a second eccentric element in connection with the second input element for rotation thereby around the second rotational axis, a second drive arm having a first end and a second end opposite the first end, the first end of the second drive arm being connected to the second eccentric element for rotation about a generally upstanding second eccentric axis of the second eccentric element, the second eccentric axis being laterally offset relative to second rotational axis for rotation thereabout, the second drive arm extending in a second direction from the first end thereof to the second end thereof, the second end of the second drive arm pivotally connecting eccentrically to a second pivot element supported for rotation about a generally upstanding second pivotal axis, such that the second pivot element will be pivoted about the second pivotal axis by the rotation of the second input element about the second rotational axis, and the second pivot element being configured for connection to a second sickle knife assembly, such that the second sickle knife assembly will be reciprocatingly moved relative to the drive (62A, 62B) by the pivoting of the second pivot element, characterized in that the first drive arm extends sidewardly within a forward portion of the cavity generally forwardly of and across the second input element, and the second drive arm extends sidewardly within a rear portion of the cavity generally rearwardly of and across the first input element.