Gearbox is relatively easy. HOld the box up whilst you remove the mount/exh mount. Replace it all with new mount. Remove holding device (Id use a jack to hold the box up).
Engine is a lot harder. Id probably either leave it til you pull the motor, or pay someone to do it LOL!
Well, err basically lift the engine off the mounts, replace mounts and then drop the engine back on the mounts. Sounds a lot easier than it is, believe me!
I will concur, its a real ball ache, i even dropped the front sub-frame a touch to get it in place......Id take it to a garage and do it.
Even i did it on a ramp and found it difficult.