Andy, it'd be easier to come up than explain it over the net.
You need to get underneath really and have a look. Based on it being probably very similar to an 80, there will be a lever - check. A rod from the lever to the gearbox - check. And a box on the side of the transmission on the OPPOSITE side to where the lever goes in. Check?
The lever has rubber bushes at one end and a slot to allow for adjustment. I found the wear in the rubber bush was enough to knock mine out of adjustment. I swapped that and suddenly it all made sense. I kept adjusting it, tightening it up and then it wasn't where I'd set it!!! So bear that in mind.
I'd have a twiddle with it to get familiar ad then maybe come back if you can't get it right. The housing thing is probably on slots so that you can loosen it and turn it a couple of degrees either way for fine tuning. I'd leave that alone for now and have a go at slacking the nut on the rod and reset the position. Set the lever in neutral, slacken the adjuster nut and move the slider a SMALL amount in one direction and see if that gets it. Helpful to have someone hold the lever in the cabin to stop it moving. There is a procedure for this which is a bit hard to understand. You are supposed to push the adjuster coming out of the box, against the detent spring slightly before nipping it. it didn't make any sense when I read that. Surely when I let go, the lever and the adjuster will just move? But I did follow that and it worked. I still don't get it. Like I said, have someone in the car so that they can tell you what's going on up there. All the movement are ack to front and you won't have a clue lying there as to what the heck is going on.
Chris