I have replaced both our minis with new speedo cables and I have to tell you that it is a fun job ............. NOT!!!!!!!!!!!

there are a few ways of doing it ....... I take it this is on the moke?????
If so it isn't as hard as on a mini I belive because you can take the bonnet up higher but the real problem is getting your hand down the back. If you have got a passenger side engine steady then I found it was easier to get the speedo cable in and out but if you are looking at the drive in the box then best bet is to remove the radiator..........Also a fun job....... when the radiator is removed you can get to the drive easily first you have to undo the screw going into the box holding the drive in there (It is a 7/16th you can get to it with an extension) undow that then screw the end of the speedo back on a bit then pull the drive out and when it is out check that the gear is still attached the main thing that happens to these is that the gear comes unattached from the drive so you can fix it by pinning it with a 1/16th drill bit and pin. and then it is all good so the rest is preety self explainetory.
Oh just my 200cents worth and sorry for the long winded answer......
Pat