I need do mine as well in the near future. Got the slide-in version from YRM's. I asked them how to fit it and came out with this plan:
1. Remove the triangular side-panels behind second-row doors.
2. Remove the fuel lines from the filter and put them out of the way
3. Undo bolts, then cut out the old one piece by piece to the left side, away from the fuel lines.
4. Jack up the floor a bit between the two C posts as it might come down a bit without the support of the crossmember
5. After painting the new one, Slide it in without the brackets attached. Slide it in with the top facing front.
6. Rotate it to slide it under the tub. For some this seems to work quite easily, others have some trouble with it.
7. Once it's in position, put in all the bolts to connect it to chassis and side rails.
8. Fix brackets and connect to rear tub.
Oh and put some nylon and duralac or something between the steel surface of the member and the aluminium of the tub. Otherwise the aluminium will corrode through in no time. There is a good chance that there are big wholes in the alu already. If so you need to repair those as well.
