Dragging this up a bit i've just replaced my gear linkage, after a similar problem and have two options for you.
rebuilding your existing one
I know somehave problems with FT being like a nanny-state, but they do have a good technial/guides section.
Or my sort of suide on a straight swap, you can probably get a good one from a scrappers for about £10-15, and saves messing about.
1. Remove gear knob, gaitor and loosen the four 10mm nylock bolts you'll find, do not fully remove them.
2. Jack car and support on axel stands at the front.
3. Remove the exhaust from it's hangers and disconnect it from the cat. U clamps on mine had 13mm bolts.
4. Remove silver heat shie;d from around the cat. The fixing are a bit strange, but a bit of WD-40 and 24mm socket should see them off easily enough, prepare for lots of dirt to drop straight into you eyes during this step especially

5. Now place the car into 4th gear, and get underneath the gear box to undo the stabiliser bar (19mm spanner/ socket) being careful not to lose the washer from the gearbox side of the bolt.
6. Undo the selector shaft using a 13mm spanner, to hold the top of the bolt whislt undoing the nut at the bottom with a 13mm socket, and pull it loose from the box, being careful not to disturd the position of the gear box rod thing.
7. Now the Haynes manual recommends removing the lower brace/ crossmember. I chose not to.
8. Step into the car and fully remove the 4 bolts loosened earlier and lower the lever as far as possible.
9. Back underneath, If you were lazy like me in step 7, negotiate the linkage toward the back of the car and out from above the crossmember and lower it down.
10. Refitment is a reversal of removal
Tips -
Make sure the gear lever is in a suitable position for 4th gear on refitting.
Do not overtighten the four nylock bolts inside the car, they will shear off!
A trolley jack is useful to hold the new linkage in up place under the gear lever if like mine your mates don't like dirty hands so won't help.
Long and short sockets are helpful to deal with various clearance issues.
I'd have taken pictures but wasn't planning on doing a guide, all sizes are from memory so are subject to change. You DO NOT have to remove the battery negativeMove to guides section perhaps.
