An Off-Plane X-ray Grating Spectrometer (OP-XGS) concept is being developed to meet the needs of the International X-ray Observatory (IXO). The OP-XGS will provide the required spectral resolution of R >3000 over the 0.3 - 1 keV band with >1000 cm2 effective collecting area, using experience gained with the current generation of reflection gratings already flown on rocket experiments. We have developed several potential configurations that meet or exceed these requirements. This paper will focus on the mechanical design and requirements for one of these configurations, the "tower" concept. This configuration mounts the grating modules to the instrument platform via a tower, allowing direct alignment with the camera module. This reduces the complexity of the alignment problem while also minimizing the overall mass of the XGS. We have developed an initial interface concept and resource requirements for this option to be reviewed by the mission teams for design drivers. We contrast the resource requirements for this concept with those required for other concepts which have been reviewed by the OP-XGS team. Further, we have identified those portions of the tower design concept that will require potential technology demonstration to reach TRL 6 prior to the Preliminary Design Review.