A novel device and method for fusions inside a forward widely tapering human disc space. A stabilizing/guiding system is driven into and against the disc space. The device is further stabilized by spreading and gripping means inside both vertebral end plates. Rod retaining members hold calibrated rod units whose adapted tips perform reaming and threading of the disc space. Subsequently, the tapered cage or implant can be inserted by a free-hand method under direct vision into the prepared and tapered bed. Rod unit divergent angulation is preferably set to match that of the disc space as well as the implants so they obtain optimal distributed purchase of vertebral bone. In one embodiment, inserts are confluent with parallel medial walls rather than their long axes, increasing torsional or lateral translational stability and simplifying placement of additional bone chips. No tubular guide means are required.