If I remember rightly how to do this, have gear lever in neutral, gear box in neutral, pop the linkage on and adjust with 1/2 mm slack. disconnect again, put gear level in reverse and then gear box in reverse, pop linkage back on, if it lining up it should pop back on easy, do the same again for 1st gear and top gear. make sure there is no more than 1/2 mm slack. then take for a test drive.
Its been a long time since I last mess about with maual gear boxes.
If its the none threaded type, then it should just pop on right away, no adjustment needed, you will know right away if its the wrong size. put gear level and box into first gear before poping on the linkage.