Be aware that the TC only slides onto the gearbox input shafts & isn't fixed in position on them.
It WILL slide off them & fall if not held in position & as you know it's very heavy. I used a T shaped piece of steel through the round hole in the bottom of the bellhousing with the tongue long enough to sit on the front of the doughnut shaped bit of the TC & holes drilled in the crosspiece of the T to suit the small bolts that hold the round cover over the round hole. The manual link below shows a 'retaining strap'
Umpteen other ways of doing it but you need it to be held on as well when refitting the box to stop it moving out of position.
If you try & refit the TC as shown in the manual with the box level it's a total b!"£$%D as I discovered the first time I did one.. If you stand it on end as jamesmartin says - I used an engine crane this time - then it's a piece of cake.
This worth a read:
http://www.landroverweb.com/Pdf-files/Manuals/Workshop-Manual-P38-Range-Rover.pdf page 655 on. See page 647 for accessing the flex to TC bolts, rotate the engine to access the 4.
And this:
http://bmwe32.masscom.net/moswald/zf4hp22_rebuild/zf4hp22_rebuild.html Try & avoid pulling the input shaft (shaft & 'A'-clutch basket in the photos) off with the bellhousing as refitting it can be fun getting it back on as it has to line up with the steel & lined plates in the clutch pack & be correctly seated to depth to be sure it's through all of them. I did this earlier this year whilst sorting various leaks on my Classic's ZF4HP22 to replace the seals on the input shaft & took the opportunity to inspect the plates for wear. Push on the shaft as you pull the housing slowly away & it should stay in position - an assistant may be of help. Note the position & orientation of bearing & washers between pump & clutch basket. 210, 211,212 in the jpat link. Use a bit of grease to hold them in place.
Note that the TC must be fitted to the gearbox AND seated to the correct depth to avoid the problem you've had as the cutouts on the rear of the TC must engage with & drive the box pump.Measured from a straightedge laid across the bellhousing mouth down to the front of any of the 4 threaded lugs on the front of the TC. Measurement can be found here in the 'depth table':
https://www.ashcroft-transmissions.co.uk/automatic-gearboxes/zf4hp22eh.html
Once fitted to the box clamp in position.
I used these for parts for mine:
https://jpat.co.uk/zf.html# exploded view here, note the rear of the box in the pics is different on the RR due to the transfer box:
https://jpat.co.uk/uploads/1/0/3/5/103549764/89__zf_1_4hp22-24.pdf (Put page 1 & page 2 next to each other)
ETA If you remove the engine then you'll be doing it with the box level & you definitely need a couple of handles to manipulate the TC. Couple of lengths of threaded rod same thread as the flex to tc bolts. It
will go back on, but clear the area of people of a delicate & easily offended nature!
