Abstract: An arrangement for a tunnel scanner includes a chassis with a first data reader structure and a second data reader structure attached thereto. The first and second data reader structures include data readers that are pre-positioned before the first and second data reader structures are attached to the chassis. Indexing features of the first and second data reader structures cooperate with corresponding indexing features of the chassis to properly position the data readers relative to the chassis. In one assembly method, one or more data reader structures having pre-positioned data readers are shipped to an assembly location for a tunnel data reader. A chassis is either provided at or shipped to the assembly location. In one configuration, the data reader structures are indexed and attached to the chassis such that each data reader is placed at a desired location and orientation with respect to the chassis.