i've changed at least three gearboxes and a minimum of two clutches in the three to four years i've owned landrovers (it might be five years), it never seems to get any easier, the bolts are always rusted in and/or rounded off no matter how recent you've had it all apart
i've also changed a couple of clutches for mates in thier landys, it's always been done in one day start to finish but it is a bloody long day, the last one i did was finished just after midnight and that was just a thrust bearing change so the gearbox was only mauled back just enough to swap the bearing
ALL bolts holding the landrover together need copperease when reassembling in the hope that it'll come apart easier the next time, make no mistake it WILL need to come apart again and half the bolts will have rusted again
clutches must be the worst job to have to tackle if it needs to be done quickly
i've no idea if it is easier with a removable crossmember really as i've not had to deal with one of those but i'll guess it is slightly easier although you'll most likely still have to remove the floor panels and gearbox tunnel to undo the top of the bellhousing
and no i don't volunteer to replace clutches, i get paid to do it
oh and if it's a Series 3 learn what the wading plug is for or you will be replacing the thrust bearing pretty frequently if you take it offroad or laning regularly