OK everyone:
Changing the dogbone mount was very easy. Just jack up car and support, jack up engine to support weight, and change dogbone mount.
Changing Gearbox supporting mount was also quite easy - take out airbox and do it (obv support gearbox with jack underneath).
Engine side supporting mount looks like it will be a bit more difficult with lots of different things having to come out (power steering reservoir, radiator reservoir etc) so just left it for now haha. It seems changing the other two was enough to get rid of the violent movement I was getting from the engine under power (mounts weredamaged on Romanian roads during snow blizzard).
Car certainly seems a bit more solid taking off in 1st, whereas before it would always feel a bit rough, if that's an accurate way to describe it. Gear changes all round seem a bit smoother (maybe because of excessive movement before). Noisier exhaust on startup for a few seconds though, but I guess this might go away once it beds down.