A dunnage conversion machine for converting an expandable pre-slit sheet stock material into a relatively less dense dunnage product includes an improved expansion assembly that provides means for adjusting the spacing between axes of rotation of components through which the sheet stock material is drawn. The adjustability enables pre-slit sheet stock materials of differing thicknesses and/or having differing slit patterns to be fed through the expansion assembly with no or minimal compression of an expanded dunnage product, jamming in the conversion machine, bunching, and/or tearing of the pre-slit sheet stock material or expanded dunnage product resulting from expansion of the pre-slit sheet stock material.