Haystack, MIT's 37-m radio telescope, was built in the early 1960s. At the time considered to be a high-performance antenna, Haystack produced a number of outstanding scientific results. The antenna, originally designed to operate at 8-10 GHz, was upgraded at various times, notably in 1993 with the addition of a deformable subreflector to allow operations at 115 GHz. Planning is now underway for a major upgrade with the replacement of the entire elevation structure that is supported on the existing yoke and tower. The new antenna should be capable of operating at up to 325 GHz. In this paper, we will describe the limitations of the original design, the solutions used in the previous upgrades, and how the lessons learned led to the approach used in the planned upgrade. The major issues limiting the further upgrade of the existing telescope were in the elevation structure; these included fabrication tolerances and gravity sag of the reflector panels, thermal lag of a ring plate supporting the reflector panels, non-repeatable behavior of the sliding joint at the elevation bearing and shear pins, and the interaction of the steel yoke and the aluminum backstructure.