Shame the Queen can't have a Jubilee every week!
I'm just going to change the inner cv joint(nearside) on mine because the shaft and outer joint are both fine.
Can't see any need to change good usable parts just for the sake of it.
Not sure on the GT but the inner joint on a 156 2.4jtd is fairly easy to change.I undid the top wishbone balljoint,the strut fork at the lower wishbone(but I was changing springs and top 'bones anyway,so the strut was removed too) and undid the six bolts that hold the driveshaft inner end,took off the cover plate,undid the circlip and off it came,eventually.Not too sure about the outer end,tho.I've read that the abs sensor is easily damaged and that the hub nut is a bit of a bugger!!But if the outer is ok,it doesn't need to be disturbed.
As I said tho,I'm not sure if the GT is the same,no doubt the clever people on here will know!
Are you sure it is actually the driveshaft?buckled wheels,worn tyres,to name but two,can also cause similar issues,just a thought.
Sorry I couldn't be more help!