A printer comprising: an array of rollers (60, 260) arranged in a first arc configuration to rollingly support a media web in a first orientation; and an array of printing elements (41, 43, 243) arranged in a second arc configuration along the first orientation and movable relative to the array of rollers (60, 260) to selectively modify a vertical space therebetween, wherein each respective printing element (41, 43, 243) is aligned directly above one of the respective rollers (60, 260) to define a printing unit; wherein a positioning structure (310, 312, 320) configured to releasably secure each printing unit at one position of a plurality of positions along the respective first and second arc configurations, wherein the array of rollers (60, 260) is supported by a first frame that comprises a pair of arcuate plates (276, 278) spaced apart from each other in a second orientation generally perpendicular to the first orientation and each respective roller (60, 260) extends between, and is supported by, the respective arcuate plates (276, 278) of the first frame, and wherein the array of printing elements (41, 43, 243) is supported by a second frame that comprises a pair of arcuate plates (246, 248) spaced apart from each other in the second orientation and each respective printing element extends between, and is supported by, the respective arcuate plates (246, 248) of the second frame, wherein the positioning structure (310, 312, 320) comprises: a first slot defined within, and extending in an arc along, each respective plate of the first frame, the first slot configured to mount each roller to be slidably movable within the first slot to one of the positions along the first arc configuration; and a second slot (310, 320) defined within, and extending in an arc along, each respective plate of the second frame, the second slot (310, 320) configured to mount each printing element (41, 43, 243) to be slidably movable within the second slot (310, 320) to one of the positions along the second arc configuration. an array of rollers (60, 260) arranged in a first arc configuration to rollingly support a media web in a first orientation; and an array of printing elements (41, 43, 243) arranged in a second arc configuration along the first orientation and movable relative to the array of rollers (60, 260) to selectively modify a vertical space therebetween, wherein each respective printing element (41, 43, 243) is aligned directly above one of the respective rollers (60, 260) to define a printing unit; wherein a positioning structure (310, 312, 320) configured to releasably secure each printing unit at one position of a plurality of positions along the respective first and second arc configurations, wherein the array of rollers (60, 260) is supported by a first frame that comprises a pair of arcuate plates (276, 278) spaced apart from each other in a second orientation generally perpendicular to the first orientation and each respective roller (60, 260) extends between, and is supported by, the respective arcuate plates (276, 278) of the first frame, and wherein the array of printing elements (41, 43, 243) is supported by a second frame that comprises a pair of arcuate plates (246, 248) spaced apart from each other in the second orientation and each respective printing element extends between, and is supported by, the respective arcuate plates (246, 248) of the second frame, wherein the positioning structure (310, 312, 320) comprises: a first slot defined within, and extending in an arc along, each respective plate of the first frame, the first slot configured to mount each roller to be slidably movable within the first slot to one of the positions along the first arc configuration; and a second slot (310, 320) defined within, and extending in an arc along, each respective plate of the second frame, the second slot (310, 320) configured to mount each printing element (41, 43, 243) to be slidably movable within the second slot (310, 320) to one of the positions along the second arc configuration. a first slot defined within, and extending in an arc along, each respective plate of the first frame, the first slot configured to mount each roller to be slidably movable within the first slot to one of the positions along the first arc configuration; and a second slot (310, 320) defined within, and extending in an arc along, each respective plate of the second frame, the second slot (310, 320) configured to mount each printing element (41, 43, 243) to be slidably movable within the second slot (310, 320) to one of the positions along the second arc configuration.